diff --git a/src/polygon_mesh/area_mesh_factory.cpp b/src/polygon_mesh/area_mesh_factory.cpp
index 276ec5ba..bee3f3d4 100644
--- a/src/polygon_mesh/area_mesh_factory.cpp
+++ b/src/polygon_mesh/area_mesh_factory.cpp
@@ -15,6 +15,7 @@ namespace {
     */
     using GridIDToObjectsMap = std::map<unsigned, std::list<const citygml::CityObject*>>;
     using GroupGridIDToObjectsMap = std::map<std::pair<unsigned, unsigned>, std::list<const citygml::CityObject*>>;
+    using GroupGridIDToObjectsWithPathMap = std::map<std::pair<unsigned, unsigned>, std::list<std::pair<const citygml::CityObject*, std::string>>>;
 
     bool shouldSkipCityObj(const citygml::CityObject& city_obj, const MeshExtractOptions& options, const std::vector<geometry::Extent>& extents) {
         if (!options.exclude_city_object_outside_extent)
@@ -169,61 +170,86 @@ namespace plateau::polygonMesh {
         AreaMeshFactory::combine(const CityModelVector& city_models, const MeshExtractOptions& options, unsigned lod,
             const plateau::geometry::GeoReference& geo_reference, const std::vector<plateau::geometry::Extent>& extents) {
 
-        const auto& gmlPath = city_models->empty() || city_models->front().expired() ? "" : city_models->front().lock()->getGmlPath();
-        std::shared_ptr <std::vector<const CityObject*>> all_primary_city_objects = std::make_shared<std::vector<const CityObject*>>();
+        // 各CityObjectとそのソースのgmlPathをペアで保持
+        std::shared_ptr<std::vector<std::pair<const CityObject*, std::string>>> all_primary_city_objects =
+            std::make_shared<std::vector<std::pair<const CityObject*, std::string>>>();
 
         const auto& _city_models = *city_models;
         for (const auto& city_model : _city_models) {
 
             if (city_model.expired()) continue; // 参照が切れている場合はスキップ
 
+            const auto& gmlPath = city_model.lock()->getGmlPath();
             auto city_objects =
                 city_model.lock()->getAllCityObjectsOfType(PrimaryCityObjectTypes::getPrimaryTypeMask());
 
-            all_primary_city_objects->insert(all_primary_city_objects->end(),
-                city_objects.begin(), city_objects.end());
+            for (const auto& city_obj : city_objects) {
+                all_primary_city_objects->emplace_back(city_obj, gmlPath);
+            }
         }
 
-        auto merged_meshes = GridMergeResult();
-
-        // メッシュ生成
-        MeshFactory mesh_factory(nullptr, options, extents, geo_reference);
-
-        // グループ内の各主要地物のループ
+        // LODレベルでグループ分けします。
+        // グループIDとグリッドIDのペアをキーとし、グリッドIDは常に0（グリッド分割なし）
+        auto group_id_to_primary_objects_map = GroupGridIDToObjectsWithPathMap();
         const auto& all_primary_city_objects_in_model = *all_primary_city_objects;
-        for (const auto& primary_object : all_primary_city_objects_in_model) {
 
-			if (options.highest_lod_only) {
-				// highest_lod_only オプションが有効な場合、最大LODのみを対象とします。
-                unsigned max_lod_in_obj = PolygonMeshUtils::max_lod_in_specification_;
-                for (unsigned target_lod = lod + 1; target_lod <= PolygonMeshUtils::max_lod_in_specification_; ++target_lod) {
-                    bool target_lod_exists =
-                        PolygonMeshUtils::findFirstPolygon(primary_object, target_lod) != nullptr;
-                    if (!target_lod_exists) {
-                        max_lod_in_obj = target_lod - 1;
-                        break;
-                    }
+        for (const auto& [primary_object, gmlPath] : all_primary_city_objects_in_model) {
+            // この CityObject について、最大でどのLODまで存在するか確認します。
+            unsigned max_lod_in_obj = PolygonMeshUtils::max_lod_in_specification_;
+            for (unsigned target_lod = lod + 1; target_lod <= PolygonMeshUtils::max_lod_in_specification_; ++target_lod) {
+                bool target_lod_exists =
+                    PolygonMeshUtils::findFirstPolygon(primary_object, target_lod) != nullptr;
+                if (!target_lod_exists) {
+                    max_lod_in_obj = target_lod - 1;
+                    break;
                 }
+            }
+
+            if (options.highest_lod_only) {
+                // highest_lod_only オプションが有効な場合、最大LODのみを対象とします。
                 if (lod != max_lod_in_obj) {
                     // 最大LOD以外はスキップします。
                     continue;
                 }
-			}
-
-            if (MeshExtractor::isTypeToSkip(primary_object->getType())) continue;
-            if (MeshExtractor::shouldContainPrimaryMesh(lod, *primary_object)) {
-                mesh_factory.addPolygonsInPrimaryCityObject(*primary_object, lod, gmlPath);
             }
 
-            if (lod >= 2) {
-                // 主要地物の子である各最小地物をメッシュに加えます。
-                auto atomic_objects = PolygonMeshUtils::getChildCityObjectsRecursive(*primary_object);
-                mesh_factory.addPolygonsInAtomicCityObjects(*primary_object, atomic_objects, lod, gmlPath);
+            // グループに追加します。
+            // grid_idは常に0（グリッド分割なし）
+            unsigned grid_id = 0;
+            unsigned group_id = max_lod_in_obj;
+            const auto group_grid_id = std::make_pair(group_id, grid_id);
+
+            if (group_id_to_primary_objects_map.find(group_grid_id) == group_id_to_primary_objects_map.end())
+                group_id_to_primary_objects_map[group_grid_id] = std::list<std::pair<const CityObject*, std::string>>();
+
+            group_id_to_primary_objects_map.at(group_grid_id).emplace_back(primary_object, gmlPath);
+        }
+
+        // グループごとにメッシュを結合します。
+        auto merged_meshes = GridMergeResult();
+
+        // グループごとのループ
+        for (const auto& [id, primary_objects] : group_id_to_primary_objects_map) {
+            // 1グループのメッシュ生成
+            MeshFactory mesh_factory(nullptr, options, extents, geo_reference);
+
+            // グループ内の各主要地物のループ
+            for (const auto& [primary_object, gmlPath] : primary_objects) {
+                if(MeshExtractor::isTypeToSkip(primary_object->getType())) continue;
+                if (MeshExtractor::shouldContainPrimaryMesh(lod, *primary_object)) {
+                    mesh_factory.addPolygonsInPrimaryCityObject(*primary_object, lod, gmlPath);
+                }
+
+                if (lod >= 2) {
+                    // 主要地物の子である各最小地物をメッシュに加えます。
+                    auto atomic_objects = PolygonMeshUtils::getChildCityObjectsRecursive(*primary_object);
+                    mesh_factory.addPolygonsInAtomicCityObjects(*primary_object, atomic_objects, lod, gmlPath);
+                }
+                mesh_factory.incrementPrimaryIndex();
             }
-            mesh_factory.incrementPrimaryIndex();
+            mesh_factory.optimizeMesh();
+            merged_meshes.emplace(id, mesh_factory.releaseMesh());
         }
-        mesh_factory.optimizeMesh();
-        merged_meshes.emplace(std::make_pair(0,0), mesh_factory.releaseMesh());
 
         return merged_meshes;
     }