diff --git a/backend/app/api/customers.py b/backend/app/api/customers.py
index b95f1be..4722ceb 100644
--- a/backend/app/api/customers.py
+++ b/backend/app/api/customers.py
@@ -103,10 +103,14 @@ async def list_customers(
             select(CustomerAssignment.customer_id, User.name)
             .join(User, CustomerAssignment.manager_id == User.id)
             .where(CustomerAssignment.customer_id.in_([c.id for c in items]), CustomerAssignment.role == "primary")
+            .order_by(CustomerAssignment.customer_id)
         )
-        mgr_map = {str(cid): name for cid, name in mgr_result.all()}
+        mgr_map: dict[str, list] = {}
+        for cid, name in mgr_result.all():
+            mgr_map.setdefault(str(cid), []).append(name)
         for item in items:
-            item.primary_manager_name = mgr_map.get(str(item.id), None)
+            names = mgr_map.get(str(item.id), [])
+            item.primary_manager_name = "、".join(names) if names else None
 
     return CustomerListResponse(
         items=items,