diff --git a/src/learn/learner.cpp b/src/learn/learner.cpp
index 1e51eeb5..a9e742a0 100644
--- a/src/learn/learner.cpp
+++ b/src/learn/learner.cpp
@@ -2537,8 +2537,26 @@ void shuffle_files_on_memory(const vector<string>& filenames,const string output
 	std::cout << "..shuffle_on_memory done." << std::endl;
 }
 
-void convert_bin(const vector<string>& filenames, const string& output_file_name, const int ply_minimum, const int ply_maximum, const int interpolate_eval, const bool check_illegal_move)
+bool fen_is_ok(Position& pos, std::string input_fen) {
+	std::string pos_fen = pos.fen();
+	std::istringstream ss_input(input_fen);
+	std::istringstream ss_pos(pos_fen);
+
+	// example : "2r4r/4kpp1/nb1np3/p2p3p/B2P1BP1/PP6/4NPKP/2R1R3 w - h6 0 24"
+	//       --> "2r4r/4kpp1/nb1np3/p2p3p/B2P1BP1/PP6/4NPKP/2R1R3"
+	std::string str_input, str_pos;
+	ss_input >> str_input;
+	ss_pos >> str_pos;
+
+	// Only compare "Piece placement field" between input_fen and pos.fen().
+	return str_input == str_pos;
+}
+
+void convert_bin(const vector<string>& filenames, const string& output_file_name, const int ply_minimum, const int ply_maximum, const int interpolate_eval, const bool check_invalid_fen, const bool check_illegal_move)
 {
+	std::cout << "check_invalid_fen=" << check_invalid_fen << std::endl;
+	std::cout << "check_illegal_move=" << check_illegal_move << std::endl;
+
 	std::fstream fs;
 	uint64_t data_size=0;
 	uint64_t filtered_size = 0;
@@ -2571,16 +2589,16 @@ void convert_bin(const vector<string>& filenames, const string& output_file_name
 			std::string value;
 			ss >> token;
 			if (token == "fen") {
-			  states = StateListPtr(new std::deque<StateInfo>(1)); // Drop old and create a new one
+				states = StateListPtr(new std::deque<StateInfo>(1)); // Drop old and create a new one
 				std::string input_fen = line.substr(4);
 				tpos.set(input_fen, false, &states->back(), Threads.main());
-				if (!tpos.pos_is_ok() || tpos.fen() != input_fen) {
+				if (check_invalid_fen && !fen_is_ok(tpos, input_fen)) {
 					ignore_flag_fen = true;
 					filtered_size_fen++;
 				}
 				else {
-			  tpos.sfen_pack(p.sfen);
-			}
+					tpos.sfen_pack(p.sfen);
+				}
 			}
 			else if (token == "move") {
 				ss >> value;
@@ -2607,7 +2625,7 @@ void convert_bin(const vector<string>& filenames, const string& output_file_name
 				}
 				p.gamePly = uint16_t(temp); // No cast here?
 				if (interpolate_eval != 0){
-				  p.score = min(3000, interpolate_eval * temp);
+					p.score = min(3000, interpolate_eval * temp);
 				}
 			}
 			else if (token == "result") {
@@ -2615,17 +2633,17 @@ void convert_bin(const vector<string>& filenames, const string& output_file_name
 				ss >> temp;
 				p.game_result = int8_t(temp); // Do you need a cast here?
 				if (interpolate_eval){
-				  p.score = p.score * p.game_result;
+					p.score = p.score * p.game_result;
 				}
 			}
 			else if (token == "e") {
-				if(!(ignore_flag_fen || ignore_flag_move || ignore_flag_ply)){
-				fs.write((char*)&p, sizeof(PackedSfenValue));
-				data_size+=1;
-				// debug
-				// std::cout<<tpos<<std::endl;
-				// std::cout<<p.score<<","<<int(p.gamePly)<<","<<int(p.game_result)<<std::endl;
-			  }
+				if (!(ignore_flag_fen || ignore_flag_move || ignore_flag_ply)) {
+					fs.write((char*)&p, sizeof(PackedSfenValue));
+					data_size+=1;
+					// debug
+					// std::cout<<tpos<<std::endl;
+					// std::cout<<p.score<<","<<int(p.gamePly)<<","<<int(p.game_result)<<std::endl;
+				}
 				else {
 					filtered_size++;
 				}
@@ -2635,7 +2653,7 @@ void convert_bin(const vector<string>& filenames, const string& output_file_name
 			}
 		}
 		std::cout << "done " << data_size << " parsed " << filtered_size << " is filtered"
-				  << " (illegal fen:" << filtered_size_fen << ", illegal move:" << filtered_size_move << ", illegal ply:" << filtered_size_ply << ")" << std::endl;
+				  << " (invalid fen:" << filtered_size_fen << ", illegal move:" << filtered_size_move << ", invalid ply:" << filtered_size_ply << ")" << std::endl;
 		ifs.close();
 	}
 	std::cout << "all done" << std::endl;
@@ -2983,6 +3001,7 @@ void learn(Position&, istringstream& is)
 	int ply_minimum = 0;
 	int ply_maximum = 114514;
 	bool interpolate_eval = 0;
+	bool check_invalid_fen = false;
 	bool check_illegal_move = false;
 	// convert teacher in pgn-extract format to Yaneura King's bin
 	bool use_convert_bin_from_pgn_extract = false;
@@ -3123,6 +3142,7 @@ void learn(Position&, istringstream& is)
 		else if (option == "convert_plain") use_convert_plain = true;
 		else if (option == "convert_bin") use_convert_bin = true;
 		else if (option == "interpolate_eval") is >> interpolate_eval;
+		else if (option == "check_invalid_fen") is >> check_invalid_fen;
 		else if (option == "check_illegal_move") is >> check_illegal_move;
 		else if (option == "convert_bin_from_pgn-extract") use_convert_bin_from_pgn_extract = true;
 		else if (option == "pgn_eval_side_to_move") is >> pgn_eval_side_to_move;
@@ -3235,7 +3255,7 @@ void learn(Position&, istringstream& is)
 	{
 		Eval::init_NNUE();
 		cout << "convert_bin.." << endl;
-		convert_bin(filenames,output_file_name, ply_minimum, ply_maximum, interpolate_eval, check_illegal_move);
+		convert_bin(filenames,output_file_name, ply_minimum, ply_maximum, interpolate_eval, check_invalid_fen, check_illegal_move);
 		return;
 		
 	}