* Market capitalisation of Topix hits another record high * Foreigners placed net buy in stocks for May 11-15, MOF * Companies announcing shareholder returns attract buying By Ayai Tomisawa TOKYO, May 21 (Reuters) - Japan's Nikkei share average rose for a fifth day on Thursday, hitting a fresh 15-year high as optimism over domestic economic growth lingered, while Panasonic Corp soared after saying it raised investment in the automotive business this fiscal year.

The Nikkei 225 rose 0.4 percent to 20,268.77 in mid-morning trade after climbing as high as 20,298.19, the highest since April 2000. The index has risen for five straight days, the longest daily winning streak in three months.

On Wednesday, the market capitalisation on the Tokyo Stock Exchange's main board hit a record high during trade, exceeding its 1989 peak of 590.9 trillion yen at one point. By 0116 GMT on Thursday, market capitalisation rose higher to 592.8 trillion yen.

"We can't simply compare now with the late 80s because the number of listed companies is different, but the fact that it hit a record high is symbolic," said Hikaru Sato, a senior technical analyst at Daiwa Securities. "It's symbolic that the stock market has restored confidence." Market observers also said that while profit-taking was likely in the short-term amid fast paced rises in the market, foreign buying should support long-term sentiment.

According to Ministry of Finance data released on Thursday morning, foreigners bought a net 187.3 billion yen worth of Japanese stocks from May 11-15.

"Foreign investors have bought Japanese stocks on hopes for strong profits and higher shareholder returns, and this trend is likely to continue," said Masashi Oda, chief investment officer at Sumitomo Mitsui Trust Bank.

Panasonic gained 4.2 percent to 1,825 yen, the highest since October 2008 after it said it would increase its investment in the automotive business industry by 50 percent to 165 billion yen for the year ending March 2016.

Following the move, Nomura Securities raised its rating to 'buy' from 'neutral,' citing sales growth prospects.

Some companies were in demand due to higher shareholder return hopes. MS&AD Insurance jumped 6.1 percent after it said it would buy back up to 10 million shares, or 1.63 percent of shares outstanding, worth up to 20 billion yen.

Yamato Holdings gained 1.4 percent after the Nikkei business daily reported that it is expected to buy back more than 10 billion yen worth of its own shares during this fiscal year through March.

The broader Topix gained 0.6 percent to 1,653.12 and the JPX-Nikkei Index 400 added 0.6 percent to 14,951.94.

(Editing by Jacqueline Wong)