diff --git a/conf.d/frontend.dev.conf b/conf.d/frontend.dev.conf
index d6e0b14..857ed7b 100644
--- a/conf.d/frontend.dev.conf
+++ b/conf.d/frontend.dev.conf
@@ -8,7 +8,7 @@
             proxy_set_header Host $host;
             proxy_set_header X-Real-IP $remote_addr;
             proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-            proxy_set_header X-Forwarded-Proto $scheme;
+            proxy_set_header X-Forwarded-Proto $forwarded_proto;
             proxy_read_timeout 86400s;
             proxy_send_timeout 86400s;
         }
diff --git a/nginx.conf b/nginx.conf
index b787822..ea2d742 100644
--- a/nginx.conf
+++ b/nginx.conf
@@ -14,6 +14,11 @@
         ''      close;
     }
 
+    map $http_x_forwarded_proto $forwarded_proto {
+        default $http_x_forwarded_proto;
+        ''      $scheme;
+    }
+
     upstream backend {
         server backend:8000;
     }
@@ -33,7 +38,7 @@
             proxy_set_header Host $host;
             proxy_set_header X-Real-IP $remote_addr;
             proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-            proxy_set_header X-Forwarded-Proto $scheme;
+            proxy_set_header X-Forwarded-Proto $forwarded_proto;
             proxy_connect_timeout 1800s;
             proxy_send_timeout 1800s;
             proxy_read_timeout 1800s;
@@ -51,7 +56,7 @@
             proxy_set_header Host $host;
             proxy_set_header X-Real-IP $remote_addr;
             proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-            proxy_set_header X-Forwarded-Proto $scheme;
+            proxy_set_header X-Forwarded-Proto $forwarded_proto;
             proxy_connect_timeout 1800s;
             proxy_send_timeout 1800s;
             proxy_read_timeout 1800s;
@@ -69,7 +74,7 @@
             proxy_set_header Host $host;
             proxy_set_header X-Real-IP $remote_addr;
             proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-            proxy_set_header X-Forwarded-Proto $scheme;
+            proxy_set_header X-Forwarded-Proto $forwarded_proto;
             proxy_connect_timeout 1800s;
             proxy_send_timeout 1800s;
             proxy_read_timeout 1800s;
@@ -84,7 +89,7 @@
             proxy_set_header Host $host;
             proxy_set_header X-Real-IP $remote_addr;
             proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-            proxy_set_header X-Forwarded-Proto $scheme;
+            proxy_set_header X-Forwarded-Proto $forwarded_proto;
         }
 
         # エージェントチャット: ファイル添付 最大 10MB
@@ -97,7 +102,7 @@
             proxy_set_header Host $host;
             proxy_set_header X-Real-IP $remote_addr;
             proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-            proxy_set_header X-Forwarded-Proto $scheme;
+            proxy_set_header X-Forwarded-Proto $forwarded_proto;
             proxy_read_timeout 86400s;
             proxy_send_timeout 86400s;
         }
@@ -110,7 +115,7 @@
             proxy_set_header Host $host;
             proxy_set_header X-Real-IP $remote_addr;
             proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-            proxy_set_header X-Forwarded-Proto $scheme;
+            proxy_set_header X-Forwarded-Proto $forwarded_proto;
             proxy_read_timeout 86400s;
             proxy_send_timeout 86400s;
         }
@@ -123,7 +128,7 @@
             proxy_set_header Host $host;
             proxy_set_header X-Real-IP $remote_addr;
             proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-            proxy_set_header X-Forwarded-Proto $scheme;
+            proxy_set_header X-Forwarded-Proto $forwarded_proto;
         }
 
         # FastAPI MCP (Streamable HTTP) — バッファリング無効でストリーミング応答を即時転送
@@ -137,7 +142,7 @@
             proxy_set_header Host $host;
             proxy_set_header X-Real-IP $remote_addr;
             proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
-            proxy_set_header X-Forwarded-Proto $scheme;
+            proxy_set_header X-Forwarded-Proto $forwarded_proto;
         }
 
         include /etc/nginx/conf.d/frontend.conf;