KOBE, Japan (Reuters) -Bank of Japan board member Toyoaki Nakamura said on Thursday the central bank must be cautious about phasing out its massive stimulus, playing down the chance of a near-term end to its negative interest rate policy. The BOJ must take time to gauge whether Japan's companies and economic structure are changing from three decades of subdued inflation and wage growth, he said. "It would be risky to change policy on the assumption that things will improve ahead in Japan's economy," Nakamura told a news conference after meeting business leaders in the western Japan city of Kobe.