* Nikkei falls 0.8 pct, Topix down 0.4 pct * Canon jumps on share buyback announcement * Investors eye US jobs data, Olympics bid outcome * Earthquake hits eastern Japan, has little effect By Tomo Uetake TOKYO, Sept 4 (Reuters) - The Nikkei average retreated from a near three-week high on Wednesday morning, hit by profit-taking after recent big gains, with many investors on the sidelines ahead of key events in coming days. The benchmark Nikkei shed 0.8 percent at 13,868.91 in midmorning trade, after advancing 4.4 percent the past two sessions. The index was up 33 percent this year, but 13 percent below its May peak. The broader Topix declined 0.4 percent to 1,144.67. After recent gains, "it's little wonder we are seeing some profit-taking today," said Mitsushige Akino, chief fund manager at Ichiyoshi Asset Management. "Most investors are opting to wait for some key events, including U.S. jobs data, the Olympics decision and Japan's revised (April-June)GDP figures, and staying on the sidelines at the moment." Tokyo is competing against Istanbul and Madrid to host the 2020 Summer Olympics, and a final decision is expected on Saturday. U.S. payroll data for August is due out on Friday and Japan's revised second quarter GDP growth numbers will come out on Monday. Trade was fairly light on Wednesday, with volume on the Nikkei at 22.5 percent of its full daily average for the past 90 days. Bucking overall weakness, Canon Inc gained as much as 4.5 percent to hit a three-week high after the world's largest digital camera maker said it will buy back up to 1.6 percent of its own shares, for a maximum of 50 billion yen ($501 million), between Wednesday and Nov. 1. It was the third-most traded stock by turnover on the main board. Other notable movers include index heavyweight Fast Retailing Co Ltd, which fell 2.8 percent. A fund manager said Nintendo Co Ltd's potential inclusion to the benchmark Nikkei weighed on the owner of Uniqlo clothing chain. Nintendo rose 2 percent. Although a strong earthquake hit eastern Japan during the morning session, it had only limited effect on the market. On Wednesday, the Bank of Japan's two-day policy meeting began. Analysts say the meeting is attracting little investor attention as no change is expected in the central bank's massive monetary stimulus launched in April.