TOKYO, May 13 (Reuters) - Japan's Nikkei benchmark stock index posted its biggest rise in more than a month and half as investors scooped up cheap stocks, with SoftBank Group leading gains.

The Nikkei share average jumped 2.64% to 26,427.65, its sharpest daily rise since March 23, rebounding from a two-month low hit in the previous session. The index lost 2.1% this week.

The broader Topix rose 1.91% to 1,864.20, but fell 2.7% for the week.

SoftBank Group provided the biggest boost to the Nikkei, surging 12.22%, even after posting a record loss at its Vision Fund investment arm, and an annual net loss of 1.7 trillion yen ($13.16 billion) for the group.

"SoftBank's big loss had been already priced in its shares so investors were not surprised by the outcome," said Shuji Hosoi, senior strategist at Daiwa Securities.

Yutaka Miura, senior technical analyst at Mizuho Securities, said investors bought SoftBank on expectations the Nasdaq would rise later in the day.

Heavyweight Tokyo Electron advanced 5.54% on the chip equipment maker's robust annual forecast for this fiscal year.

Nissan Motor slipped 2.93% after the automaker warned of flat operating profit this fiscal year, far below analysts' expectations.

There were 174 advancers on the Nikkei index against 49 decliners.

The volume of shares traded on the Tokyo Stock Exchange's main board was 1.69 billion, compared to the average of 1.23 billion in the past 30 days.

($1 = 129.1400 yen) (Reporting by Junko Fujita; Editing by Vinay Dwivedi)