The Nikkei stock index finished Wednesday at a five-month high, as fears the Bank of Japan will soon alter its ultraloose monetary policy were eased after its governor offered few hints of a change the day before. The 225-issue Nikkei Stock Average ended up 456.55 points, or 1.37 percent, from Tuesday at 33,675.94, its highest finish since July 3. The broader Topix index finished 15.57 points, or 0.67 percent, higher at 2,349.38. On the top-tier Prime Market, gainers were led by marine transportation, machinery and chemical issues.