diff --git a/src/main/java/org/embulk/input/google_ads/GoogleAdsReporter.java b/src/main/java/org/embulk/input/google_ads/GoogleAdsReporter.java
index 10b252b..df2e40d 100644
--- a/src/main/java/org/embulk/input/google_ads/GoogleAdsReporter.java
+++ b/src/main/java/org/embulk/input/google_ads/GoogleAdsReporter.java
@@ -7,9 +7,14 @@
 import com.fasterxml.jackson.databind.node.JsonNodeType;
 import com.fasterxml.jackson.databind.node.ObjectNode;
 import com.google.ads.googleads.lib.GoogleAdsClient;
+import com.google.ads.googleads.v16.resources.CustomerName;
+import com.google.ads.googleads.v16.services.CustomerServiceClient;
 import com.google.ads.googleads.v16.services.GoogleAdsRow;
 import com.google.ads.googleads.v16.services.GoogleAdsServiceClient;
+import com.google.ads.googleads.v16.services.ListAccessibleCustomersRequest;
 import com.google.ads.googleads.v16.services.SearchGoogleAdsRequest;
+import com.google.ads.googleads.v16.services.SearchGoogleAdsStreamRequest;
+import com.google.ads.googleads.v16.services.SearchGoogleAdsStreamResponse;
 import com.google.auth.oauth2.UserCredentials;
 import com.google.common.base.CaseFormat;
 import com.google.protobuf.Descriptors;
@@ -23,6 +28,7 @@
 import org.slf4j.LoggerFactory;
 
 import java.util.ArrayList;
+import java.util.Collection;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
@@ -36,10 +42,8 @@ public class GoogleAdsReporter
     private final Logger logger = LoggerFactory.getLogger(GoogleAdsReporter.class);
     private final PluginTask task;
     private final UserCredentials credentials;
+    private final ObjectMapper mapper = new ObjectMapper();
     private GoogleAdsClient client;
-    private ObjectMapper mapper = new ObjectMapper();
-
-    private Iterable<GoogleAdsServiceClient.SearchPage> searchResult;
 
     public GoogleAdsReporter(PluginTask task)
     {
@@ -60,7 +64,7 @@ private Iterable<GoogleAdsServiceClient.SearchPage> search(Map<String, String> p
         String query = buildQuery(task, params);
         logger.info(query);
         SearchGoogleAdsRequest request = buildRequest(task, query);
-        GoogleAdsServiceClient googleAdsService = client.getVersion16().createGoogleAdsServiceClient();
+        GoogleAdsServiceClient googleAdsService = client.getLatestVersion().createGoogleAdsServiceClient();
         GoogleAdsServiceClient.SearchPagedResponse response = googleAdsService.search(request);
         return response.iteratePages();
     }
@@ -280,14 +284,77 @@ public List<String> buildWhereClauseConditions(PluginTask task, Map<String, Stri
     }
 
     public void connect()
+    {
+        this.client = buildClient(task.getLoginCustomerId().orElseGet(() -> getLoginCustomerId(task.getCustomerId())));
+    }
+
+    private Long getLoginCustomerId(String customerId)
+    {
+        List<Long> loginCustomerIds = getLoginCustomerIds(customerId);
+        if (loginCustomerIds.isEmpty()) {
+            throw new RuntimeException("login customer not found [customer id: " + customerId + "]");
+        }
+        if (loginCustomerIds.size() > 1) {
+            logger.info("multiple login customers found [login customer ids: {}]", loginCustomerIds.stream().map(Object::toString).collect(Collectors.joining(", ")));
+        }
+        Long loginCustomerId = loginCustomerIds.get(0);
+        logger.info("use this customer [customer id: {}, login customer id: {}] to login", customerId, loginCustomerId);
+        return loginCustomerId;
+    }
+
+    private List<Long> getLoginCustomerIds(String customerId)
+    {
+        try (CustomerServiceClient client = buildClient(null).getLatestVersion().createCustomerServiceClient()) {
+            return client.listAccessibleCustomers(ListAccessibleCustomersRequest.newBuilder().build())
+                    .getResourceNamesList()
+                    .stream()
+                    .map(CustomerName::parse)
+                    .map(CustomerName::getCustomerId)
+                    .map(this::getLoginCustomerClients)
+                    .flatMap(Collection::stream)
+                    .filter(loginCustomerClient -> loginCustomerClient.customerClientId.equals(customerId))
+                    .map(loginCustomerClient -> Long.valueOf(loginCustomerClient.loginCustomerId))
+                    .collect(Collectors.toList());
+        }
+    }
+
+    private List<LoginCustomerClient> getLoginCustomerClients(String customerId)
+    {
+        try (GoogleAdsServiceClient client = buildClient(Long.valueOf(customerId)).getLatestVersion().createGoogleAdsServiceClient()) {
+            return client.searchStreamCallable().call(SearchGoogleAdsStreamRequest.newBuilder()
+                            .setCustomerId(customerId)
+                            .setQuery("SELECT customer_client.id FROM customer_client")
+                            .build())
+                    .stream()
+                    .map(SearchGoogleAdsStreamResponse::getResultsList)
+                    .flatMap(Collection::stream)
+                    .map(GoogleAdsRow::getCustomerClient)
+                    .map(customerClient -> new LoginCustomerClient(customerId, customerClient.getId()))
+                    .collect(Collectors.toList());
+        }
+    }
+
+    private static class LoginCustomerClient
+    {
+        LoginCustomerClient(String loginCustomerId, Long customerClientId)
+        {
+            this.loginCustomerId = loginCustomerId;
+            this.customerClientId = String.valueOf(customerClientId);
+        }
+
+        final String loginCustomerId;
+        final String customerClientId;
+    }
+
+    private GoogleAdsClient buildClient(Long loginCustomerId)
     {
         GoogleAdsClient.Builder builder = GoogleAdsClient.newBuilder()
                 .setDeveloperToken(task.getDeveloperToken())
                 .setCredentials(credentials);
-        if (task.getLoginCustomerId().isPresent()) {
-            builder.setLoginCustomerId(Long.parseLong(task.getLoginCustomerId().get()));
+        if (loginCustomerId != null) {
+            builder.setLoginCustomerId(loginCustomerId);
         }
-        this.client = builder.build();
+        return builder.build();
     }
 
     private String buildWhereClauseConditionsForChangeEvent(String startDateTime)
diff --git a/src/main/java/org/embulk/input/google_ads/PluginTask.java b/src/main/java/org/embulk/input/google_ads/PluginTask.java
index ced63a8..bad94d8 100644
--- a/src/main/java/org/embulk/input/google_ads/PluginTask.java
+++ b/src/main/java/org/embulk/input/google_ads/PluginTask.java
@@ -15,7 +15,7 @@ public interface PluginTask extends Task
 
     @Config("login_customer_id")
     @ConfigDefault("null")
-    Optional<String> getLoginCustomerId();
+    Optional<Long> getLoginCustomerId();
 
     @Config("client_id")
     String getClientId();