Japan's Nikkei falls on half-yearly portfolio adjustment

TOKYO, Sept 30 (Reuters) - Japan's Nikkei share average fell on Tuesday as investors adjusted their portfolios and corporates stayed away from buybacks at the end of the first half of the nation's fiscal year.

As of 0145 GMT, the Nikkei .N225 was down 0.1% at 44,996.05. The broader Topix .TOPX edged down 0.08% at 3,128.46.

"Today's decline does not mean the market sentiment has weakened. This kind of adjustment associated with the end of the first half of the year may continue tomorrow," said Shoichi Arisawa, general manager of the investment research department at IwaiCosmo Securities.

"The market was dragged lower by a lack of corporate buying of their own stocks at the end of the fiscal half."

Corporate share buybacks this year are at record levels in Japan as domestic firms moved to boost investor returns on the back of corporate governance reform, helping the Nikkei and the Topix to hit their peaks.

The market is also cautious ahead of the release of the crucial U.S. jobs report later this week and the outcome of the Liberal Democratic Party's leadership election on Saturday, said Arisawa.

Chip-testing equipment maker Advantest 6857.T fell 1.39% and technology start-up investor SoftBank Group 9984.T lost 1.65%. Uniqlo-brand owner Fast Retailing 9983.T slipped 0.64%.

Energy explorers .IMING.T lost 3.4% to become the worst performer on the Tokyo Stock Exchange's 33 industry sub-indexes.

On the other hand, the insurance sector .IOINSU.T gained 0.78% to become the top-performing industry index.

Infrastructure services provider Ebara 6361.T jumped 5.7% to become the top percentage gainer on the Nikkei.

Drug maker Sumitomo Pharma 4506.T gained 3.7%.

Of more than 1,600 stocks trading on the TSE's prime section, 24% rose and 71% fell, and 3% traded flat.