TOKYO, April 21 (Reuters) - Japan's Nikkei share average inched lower on Friday, erasing early gains driven by the strong performance of chip-related shares, as investors were cautions about making active bets ahead of Bank of Japan's policy meeting.

The index was down 0.07% to 28,638.24 by the midday break, after rising to 28,778.37, its highest level since Aug. 26.

For the week, the index is set to rise 0.51%, marking the second straight week of gains.

The broader Topix slipped 0.06% to 2,038.45 and is poised to rise 0.98% for the week.

"Gains on the Nikkei were capped as investors awaited the outcome of the BOJ's policy meeting. They were also eying corporate outlook as the earnings season kicked off in Japan and the U.S." said Yugo Tsuboi, a senior strategist at Daiwa Securities.

"But the trend that investors seek to buy undervalued stocks has not changed."

The BOJ is scheduled to hold a two-day meeting next week where some market participants expect the central bank to tweak its yield curve control policy, which controls the movement of the benchmark 10-year government bonds.

Uniqlo brand owner Fast Retailing Co Ltd fell 1.29% to become the biggest drag on the Nikkei. Technology investor SoftBank Group Corp lost 1.98%.

The banking sector lost 1.44% to become the worst performer among 33 industry sub-indexes on the Tokyo Stock Exchange, followed by energy explorers, which lost 1.1%.

Chip-making equipment maker Tokyo Electron Ltd rose 2.44% to become the biggest support to the Nikkei. Chip-testing equipment maker Advantest Corp was up 4.92% .

Precision machine maker Disco Corp surged 13.09% to become the top gainer on the TSE's prime market after it posted a record group annual operating profit. (Reporting by Junko Fujita; Editing by Sonia Cheema)