diff --git a/agent/platform.go b/agent/platform.go
index d740494..aceeee7 100644
--- a/agent/platform.go
+++ b/agent/platform.go
@@ -35,6 +35,16 @@ func NewPlatform(ctx context.Context, ignoreContainer *regexp.Regexp) (platform.
 		}
 		return ecs.NewECSPlatform(ctx, metadataURI, executionEnv, ignoreContainer)
 
+	// experimental : on AWS ECS External Instance, `AWS_EXECUTION_ENV` is not defined.
+	// follow user's `MACKEREL_CONTAINER_PLATFORM` setting and using unique value that does not interfere with AWS.
+	case platform.ECSExternal:
+		metadataURI, err := getEnvValue("ECS_CONTAINER_METADATA_URI")
+		if err != nil {
+			return nil, err
+		}
+		executionEnv := ecs.ExecutionEnvExternal
+		return ecs.NewECSPlatform(ctx, metadataURI, executionEnv, ignoreContainer)
+
 	case platform.Kubernetes:
 		useReadOnlyPort := true
 		insecureTLS := false
diff --git a/platform/ecs/ecs.go b/platform/ecs/ecs.go
index d722bac..8927755 100644
--- a/platform/ecs/ecs.go
+++ b/platform/ecs/ecs.go
@@ -21,6 +21,9 @@ import (
 const (
 	executionEnvFargate = "AWS_ECS_FARGATE"
 	executionEnvEC2     = "AWS_ECS_EC2"
+
+	// ExecutionEnvExternal : (experimental) It is a definition that is handled internally, not an environment variable.
+	ExecutionEnvExternal = "ECS_EXTERNAL"
 )
 
 var (
@@ -123,6 +126,8 @@ func resolveProvider(executionEnv string) (provider, error) {
 		return fargateProvider, nil
 	case executionEnvEC2:
 		return ecsProvider, nil
+	case ExecutionEnvExternal:
+		return externalProvider, nil
 	default:
 		return provider("UNKNOWN"), fmt.Errorf("unknown execution env: %q", executionEnv)
 	}
diff --git a/platform/ecs/ecs_test.go b/platform/ecs/ecs_test.go
index e83028d..1d8af27 100644
--- a/platform/ecs/ecs_test.go
+++ b/platform/ecs/ecs_test.go
@@ -39,6 +39,7 @@ func TestResolveProvider(t *testing.T) {
 	}{
 		{"AWS_ECS_FARGATE", fargateProvider},
 		{"AWS_ECS_EC2", ecsProvider},
+		{"ECS_EXTERNAL", externalProvider},
 		{"unknown", provider("UNKNOWN")},
 		{"", provider("UNKNOWN")},
 	}
diff --git a/platform/ecs/provider.go b/platform/ecs/provider.go
index f7429f3..bf33e37 100644
--- a/platform/ecs/provider.go
+++ b/platform/ecs/provider.go
@@ -6,4 +6,6 @@ type provider string
 const (
 	ecsProvider     provider = "ecs"
 	fargateProvider provider = "fargate"
+	// experimental
+	externalProvider provider = "external"
 )
diff --git a/platform/ecs/spec_test.go b/platform/ecs/spec_test.go
index 7a99b18..c4a1304 100644
--- a/platform/ecs/spec_test.go
+++ b/platform/ecs/spec_test.go
@@ -20,6 +20,7 @@ func TestGenerateSpec(t *testing.T) {
 		{"taskmetadata/testdata/metadata_ec2_host.json", ecsProvider},
 		{"taskmetadata/testdata/metadata_ec2_awsvpc.json", ecsProvider},
 		{"taskmetadata/testdata/metadata_fargate.json", fargateProvider},
+		{"taskmetadata/testdata/metadata_external.json", externalProvider},
 	}
 
 	var path string
diff --git a/platform/ecs/taskmetadata/testdata/metadata_external.json b/platform/ecs/taskmetadata/testdata/metadata_external.json
new file mode 100644
index 0000000..1dfc454
--- /dev/null
+++ b/platform/ecs/taskmetadata/testdata/metadata_external.json
@@ -0,0 +1,49 @@
+{
+    "Cluster": "test-clusrer",
+    "TaskARN": "arn:aws:ecs:ap-northeast-1:999999999999:task/task-id",
+    "Family": "test-external",
+    "Revision": "4",
+    "DesiredStatus": "RUNNING",
+    "KnownStatus": "RUNNING",
+    "Limits": {
+      "CPU": 0.25,
+      "Memory": 256
+    },
+    "PullStartedAt": "2022-03-14T06:44:39.928830311Z",
+    "PullStoppedAt": "2022-03-14T06:44:42.387434211Z",
+    "LaunchType": "EXTERNAL",
+    "Containers": [
+      {
+        "DockerId": "ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff",
+        "Name": "mackerel-container-agent",
+        "DockerName": "ecs-test-cluster-1-mackerel-container-agent-ffffffffffffffffffff",
+        "Image": "mackerel/mackerel-container-agent:latest",
+        "ImageID": "sha256:ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff",
+        "Labels": {
+          "com.amazonaws.ecs.cluster": "test-cluster",
+          "com.amazonaws.ecs.container-name": "mackerel-container-agent",
+          "com.amazonaws.ecs.task-arn": "arn:aws:ecs:ap-northeast-1:999999999999:task/task-id",
+          "com.amazonaws.ecs.task-definition-family": "test-fargate",
+          "com.amazonaws.ecs.task-definition-version": "1"
+        },
+        "DesiredStatus": "RUNNING",
+        "KnownStatus": "RUNNING",
+        "Limits": {
+          "CPU": 0,
+          "Memory": 128
+        },
+        "CreatedAt": "2019-03-29T02:54:57.61447652Z",
+        "StartedAt": "2019-03-29T02:54:58.346799541Z",
+        "Type": "NORMAL",
+        "Networks": [
+          {
+            "NetworkMode": "awsvpc",
+            "IPv4Addresses": [
+              "172.17.0.2"
+            ]
+          }
+        ]
+      }
+    ]
+  }
+  
\ No newline at end of file
diff --git a/platform/types.go b/platform/types.go
index d9da17f..f0eb364 100644
--- a/platform/types.go
+++ b/platform/types.go
@@ -12,4 +12,6 @@ const (
 	Kubernetes   Type = "kubernetes"
 	EKSOnFargate Type = "eks_fargate"
 	None         Type = "none"
+	// experimental
+	ECSExternal Type = "ecs_external"
 )