* Investors risk-averse stances ease - traders

* Mitsubishi Heavy climbs on F-35 progress report

By Ayai Tomisawa

TOKYO, Feb 16 (Reuters) - Japan's Nikkei share average rose in choppy trade on Tuesday after posting a sharp rebound the previous day, with SoftBank Group Corp leading gains after investors took heart from its share buyback announcement.

SoftBank, a large index constituent, contributed a hefty 69 points to the Nikkei benchmark, which was trading in negative territory before SoftBank shares rose 14 percent in the early morning. The telecoms conglomerate announced its biggest ever share buyback, saying it would spend up to 500 billion yen ($4.4 billion) to purchase as much as 14.2 percent of its own shares.

At 0138 GMT, the Nikkei rose 0.4 percent to 16,087.68 after falling to as low as 15,809.58 earlier. The Japanese market has suffered a roller-coaster ride recently, with the Nikkei tumbling more than 11 percent last week and rebounding 7.2 percent on Monday.

The market seems to have stabilised after oil prices rebounded and the dollar stood high against the yen. U.S. oil prices jumped back above $30 a barrel late on Monday as news of a rare private meeting of top officials from the world's biggest oil producers spurred speculation of an eventual deal to tackle a deep supply glut.

"Investors' risk-off stances have slowed down because of these external factors," said Chihiro Ohta, general manager at investment research and investor services at SMBC Nikko Securities, adding that the worst seems to be over.

As investors' risk-aversion eased, demand for financials picked up. Mitsubishi UFJ Financial Group gained 3.6 percent and Mizuho Financial Group added 3.1 percent. Nomura Holdings rose 2.5 percent and Daiwa Securities advanced 2.1 percent.

Mitsubishi Heavy Industries Ltd climbed more than 5.0 percent after the Nikkei business daily reported that the company has begun final assembly and checkout on Lockheed Martin's F-35A stealth fighter jet.

The broader Topix rose 0.6 percent to 1,300.14 and the JPX-Nikkei Index 400 added 0.6 percent to 11,741.47.

(Editing by Sam Holmes)