Japanese Finance Minister Masajuro Shiokawa said Tuesday that the recent rise in stock prices is partly due to buy-back of shares short-sold ahead of book closing time, adding that the nation's economy must improve for the rise to be more than temporary. He added that that the market was also seeing improvement among companies and financial institutions. Economics Minister Heizo Takenaka warned against complacency following the Nikkei's surge in recent sessions, saying daily stock market swings should not be basis for government policy.