TOKYO, May 7 (Xinhua) -- Tokyo stocks opened flat Monday as investors both bought on the back of Wall Street's gains last week and sold owing to the yen's rise against the U.S. dollar.

The 225-issue Nikkei Stock Average dropped 40.15 points, or 0.18 percent, from Wednesday to 22,432.63, in the first 15 minutes of trading.

The broader Topix index of all First Section issues on the Tokyo Stock Exchange, meanwhile, fell 2.61 points, or 0.15 percent, to 1,768.91.

Security and precision instruments issues comprised those that lost ground, while oil and coal product and iron and steel issues led gainers in the opening minutes after the morning bell.