diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0c2617d6..e7b4779a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -277,6 +277,7 @@ target_sources(momo
     src/momo_version.cpp
     src/util.cpp
     src/watchdog.cpp
+    src/ssl_verifier.cpp
     src/ayame/ayame_server.cpp
     src/ayame/ayame_websocket_client.cpp
     src/p2p/p2p_connection.cpp
diff --git a/src/ayame/ayame_websocket_client.cpp b/src/ayame/ayame_websocket_client.cpp
index 137acc2c..46dfbfec 100644
--- a/src/ayame/ayame_websocket_client.cpp
+++ b/src/ayame/ayame_websocket_client.cpp
@@ -1,9 +1,13 @@
 #include "ayame_websocket_client.h"
 
+// boost
 #include <boost/beast/websocket/stream.hpp>
+
+// json
 #include <nlohmann/json.hpp>
 
-#include "../momo_version.h"
+#include "momo_version.h"
+#include "ssl_verifier.h"
 #include "url_parts.h"
 #include "util.h"
 
@@ -28,7 +32,7 @@ bool AyameWebsocketClient::parseURL(URLParts& parts) const {
 
 boost::asio::ssl::context AyameWebsocketClient::createSSLContext() const {
   boost::asio::ssl::context ctx(boost::asio::ssl::context::tlsv12);
-  ctx.set_default_verify_paths();
+  //ctx.set_default_verify_paths();
   ctx.set_options(boost::asio::ssl::context::default_workarounds |
                   boost::asio::ssl::context::no_sslv2 |
                   boost::asio::ssl::context::no_sslv3 |
@@ -72,10 +76,18 @@ void AyameWebsocketClient::reset() {
 
   if (parseURL(parts_)) {
     auto ssl_ctx = createSSLContext();
-    boost::beast::websocket::stream<
-        boost::asio::ssl::stream<boost::asio::ip::tcp::socket>>
-        wss(ioc_, ssl_ctx);
     ws_.reset(new Websocket(ioc_, std::move(ssl_ctx)));
+    ws_->nativeSecureSocket().next_layer().set_verify_mode(
+        boost::asio::ssl::verify_peer);
+    ws_->nativeSecureSocket().next_layer().set_verify_callback(
+        [](bool preverified, boost::asio::ssl::verify_context& ctx) {
+          if (preverified) {
+            return true;
+          }
+          X509* cert = X509_STORE_CTX_get_current_cert(ctx.native_handle());
+          return SSLVerifier::VerifyX509(cert);
+        });
+
     // SNI の設定を行う
     if (!SSL_set_tlsext_host_name(
             ws_->nativeSecureSocket().next_layer().native_handle(),
diff --git a/src/rtc/manager.cpp b/src/rtc/manager.cpp
index dcda1e48..bccb224b 100644
--- a/src/rtc/manager.cpp
+++ b/src/rtc/manager.cpp
@@ -17,6 +17,7 @@
 #include "modules/video_capture/video_capture_factory.h"
 #include "observer.h"
 #include "rtc_base/logging.h"
+#include "rtc_base/openssl_certificate.h"
 #include "rtc_base/ssl_adapter.h"
 #include "scalable_track_source.h"
 #include "util.h"
@@ -41,6 +42,8 @@
 #include "hw_video_decoder_factory.h"
 #endif
 
+#include "ssl_verifier.h"
+
 RTCManager::RTCManager(
     ConnectionSettings conn_settings,
     rtc::scoped_refptr<ScalableVideoTrackSource> video_track_source,
@@ -191,6 +194,15 @@ void RTCManager::SetDataManager(RTCDataManager* data_manager) {
   _data_manager = data_manager;
 }
 
+class RTCSSLVerifier : public rtc::SSLCertificateVerifier {
+ public:
+  RTCSSLVerifier() {}
+  bool Verify(const rtc::SSLCertificate& certificate) override {
+    return SSLVerifier::VerifyX509(
+        static_cast<const rtc::OpenSSLCertificate&>(certificate).x509());
+  }
+};
+
 std::shared_ptr<RTCConnection> RTCManager::createConnection(
     webrtc::PeerConnectionInterface::RTCConfiguration rtc_config,
     RTCMessageSender* sender) {
@@ -198,9 +210,17 @@ std::shared_ptr<RTCConnection> RTCManager::createConnection(
   rtc_config.sdp_semantics = webrtc::SdpSemantics::kUnifiedPlan;
   std::unique_ptr<PeerConnectionObserver> observer(
       new PeerConnectionObserver(sender, _receiver, _data_manager));
+  webrtc::PeerConnectionDependencies dependencies(observer.get());
+
+  // WebRTC の SSL 接続の検証は自前のルート証明書(rtc_base/ssl_roots.h)でやっていて、
+  // その中に Let's Encrypt の証明書が無いため、接続先によっては接続できないことがある。
+  //
+  // それを解消するために tls_cert_verifier を設定して自前で検証を行う。
+  dependencies.tls_cert_verifier =
+      std::unique_ptr<rtc::SSLCertificateVerifier>(new RTCSSLVerifier());
+
   rtc::scoped_refptr<webrtc::PeerConnectionInterface> connection =
-      _factory->CreatePeerConnection(rtc_config, nullptr, nullptr,
-                                     observer.get());
+      _factory->CreatePeerConnection(rtc_config, std::move(dependencies));
   if (!connection) {
     RTC_LOG(LS_ERROR) << __FUNCTION__ << ": CreatePeerConnection failed";
     return nullptr;
diff --git a/src/sora/sora_websocket_client.cpp b/src/sora/sora_websocket_client.cpp
index 4a92cc4e..2aa9c05f 100644
--- a/src/sora/sora_websocket_client.cpp
+++ b/src/sora/sora_websocket_client.cpp
@@ -10,6 +10,7 @@
 #include <nlohmann/json.hpp>
 
 #include "momo_version.h"
+#include "ssl_verifier.h"
 #include "url_parts.h"
 #include "util.h"
 
@@ -34,7 +35,7 @@ bool SoraWebsocketClient::parseURL(URLParts& parts) const {
 
 boost::asio::ssl::context SoraWebsocketClient::createSSLContext() const {
   boost::asio::ssl::context ctx(boost::asio::ssl::context::tlsv12);
-  ctx.set_default_verify_paths();
+  //ctx.set_default_verify_paths();
   ctx.set_options(boost::asio::ssl::context::default_workarounds |
                   boost::asio::ssl::context::no_sslv2 |
                   boost::asio::ssl::context::no_sslv3 |
@@ -74,10 +75,18 @@ void SoraWebsocketClient::reset() {
 
   if (parseURL(parts_)) {
     auto ssl_ctx = createSSLContext();
-    boost::beast::websocket::stream<
-        boost::asio::ssl::stream<boost::asio::ip::tcp::socket>>
-        wss(ioc_, ssl_ctx);
     ws_.reset(new Websocket(ioc_, std::move(ssl_ctx)));
+    ws_->nativeSecureSocket().next_layer().set_verify_mode(
+        boost::asio::ssl::verify_peer);
+    ws_->nativeSecureSocket().next_layer().set_verify_callback(
+        [](bool preverified, boost::asio::ssl::verify_context& ctx) {
+          if (preverified) {
+            return true;
+          }
+          X509* cert = X509_STORE_CTX_get_current_cert(ctx.native_handle());
+          return SSLVerifier::VerifyX509(cert);
+        });
+
     // SNI の設定を行う
     if (!SSL_set_tlsext_host_name(
             ws_->nativeSecureSocket().next_layer().native_handle(),
diff --git a/src/ssl_verifier.cpp b/src/ssl_verifier.cpp
new file mode 100644
index 00000000..cb0c0bb9
--- /dev/null
+++ b/src/ssl_verifier.cpp
@@ -0,0 +1,115 @@
+#include "ssl_verifier.h"
+
+// webrtc
+#include <rtc_base/logging.h>
+#include <rtc_base/openssl_utility.h>
+#include <rtc_base/ssl_roots.h>
+
+// openssl
+#include <openssl/x509v3.h>
+
+// boost
+#include <boost/asio/connect.hpp>
+#include <boost/asio/io_context.hpp>
+#include <boost/asio/ip/tcp.hpp>
+
+bool SSLVerifier::AddCert(const std::string& pem, X509_STORE* store) {
+  BIO* bio = BIO_new_mem_buf(pem.c_str(), pem.size());
+  if (bio == nullptr) {
+    RTC_LOG(LS_ERROR) << "BIO_new_mem_buf failed";
+    return false;
+  }
+  X509* cert = PEM_read_bio_X509(bio, nullptr, nullptr, nullptr);
+  if (cert == nullptr) {
+    BIO_free(bio);
+    RTC_LOG(LS_ERROR) << "PEM_read_bio_X509 failed";
+    return false;
+  }
+  int r = X509_STORE_add_cert(store, cert);
+  if (r == 0) {
+    X509_free(cert);
+    BIO_free(bio);
+    RTC_LOG(LS_ERROR) << "X509_STORE_add_cert failed";
+    return false;
+  }
+  X509_free(cert);
+  BIO_free(bio);
+  return true;
+}
+
+// rtc_base/openssl_utility.cc を今回の用途に合わせたもの
+bool SSLVerifier::LoadBuiltinSSLRootCertificates(X509_STORE* store) {
+  int count_of_added_certs = 0;
+  for (size_t i = 0;
+       i < sizeof(kSSLCertCertificateList) / sizeof(kSSLCertCertificateList[0]);
+       i++) {
+    const unsigned char* cert_buffer = kSSLCertCertificateList[i];
+    size_t cert_buffer_len = kSSLCertCertificateSizeList[i];
+    X509* cert = d2i_X509(nullptr, &cert_buffer,
+                          cert_buffer_len);  // NOLINT
+    if (cert) {
+      int return_value = X509_STORE_add_cert(store, cert);
+      if (return_value == 0) {
+        RTC_LOG(LS_WARNING) << "Unable to add certificate.";
+      } else {
+        count_of_added_certs++;
+      }
+      X509_free(cert);
+    }
+  }
+  return count_of_added_certs > 0;
+}
+
+bool SSLVerifier::VerifyX509(X509* x509) {
+  {
+    char subject_name[256];
+    X509_NAME_oneline(X509_get_subject_name(x509), subject_name, 256);
+    RTC_LOG(LS_INFO) << "Verifying " << subject_name;
+  }
+
+  X509_STORE* store = nullptr;
+  X509_STORE_CTX* ctx = nullptr;
+
+  struct Guard {
+    std::function<void()> f;
+    Guard(std::function<void()> f) : f(std::move(f)) {}
+    ~Guard() { f(); }
+  };
+  Guard guard([&]() {
+    // nullptr を渡しても何もしない
+    X509_STORE_CTX_free(ctx);
+    X509_STORE_free(store);
+  });
+
+  store = X509_STORE_new();
+  if (store == nullptr) {
+    RTC_LOG(LS_ERROR) << "X509_STORE_new failed";
+    return false;
+  }
+
+  // WebRTC が用意しているルート証明書の設定
+  LoadBuiltinSSLRootCertificates(store);
+  // デフォルト証明書のパスの設定
+  X509_STORE_set_default_paths(store);
+  RTC_LOG(LS_INFO) << "default cert file: " << X509_get_default_cert_file();
+
+  ctx = X509_STORE_CTX_new();
+  if (ctx == nullptr) {
+    RTC_LOG(LS_ERROR) << "X509_STORE_CTX_new failed";
+    return false;
+  }
+  int r;
+  r = X509_STORE_CTX_init(ctx, store, x509, nullptr);
+  if (r == 0) {
+    RTC_LOG(LS_ERROR) << "X509_STORE_CTX_init failed";
+    return false;
+  }
+  r = X509_verify_cert(ctx);
+  if (r <= 0) {
+    RTC_LOG(LS_INFO) << "X509_verify_cert failed: r=" << r << " message="
+                     << X509_verify_cert_error_string(
+                            X509_STORE_CTX_get_error(ctx));
+    return false;
+  }
+  return true;
+}
diff --git a/src/ssl_verifier.h b/src/ssl_verifier.h
new file mode 100644
index 00000000..c1b08387
--- /dev/null
+++ b/src/ssl_verifier.h
@@ -0,0 +1,21 @@
+#ifndef SSL_VERIFIER_H_INCLUDED
+#define SSL_VERIFIER_H_INCLUDED
+
+#include <string>
+
+// openssl
+#include <openssl/ssl.h>
+
+// 自前で SSL の証明書検証を行うためのクラス
+class SSLVerifier {
+ public:
+  static bool VerifyX509(X509* x509);
+
+ private:
+  // PEM 形式のルート証明書を追加する
+  static bool AddCert(const std::string& pem, X509_STORE* store);
+  // WebRTC の組み込みルート証明書を追加する
+  static bool LoadBuiltinSSLRootCertificates(X509_STORE* store);
+};
+
+#endif  // SSL_VERIFIER_H_INCLUDED