* SoftBank adds hefty gains to Nikkei

* Mining shares outperform

By Ayai Tomisawa

TOKYO, May 22 (Reuters) - Japan's Nikkei share average rose on Monday morning following gains in U.S. shares, but the dollar's weakness and U.S. political turmoil kept investors nervous and limited gains in the market.

The Nikkei rose 0.3 percent to 19,653.32 in midmorning trade.

Meanwhile, index-heavyweight SoftBank Group Corp rose more than 2 percent and added a hefty positive 20 points to the Nikkei benchmark index after raising over $93 billion to invest in technology sectors with Saudi Arabia's main sovereign wealth fund.

Traders said that with Wall Street gaining ground, investor risk-aversion in the stock market has receded somewhat, but they remain cautious in the currency and bonds markets - limiting the upside.

"It's too early for investors to chase the market higher," said Yutaka Miura, a senior technical analyst at Mizuho Securities, adding that concerns that U.S. President Donald Trump's economic policies will be undermined by Washington's political turmoil have kept investors nervous.

Exporters were mixed, with the dollar staying on the defensive. The dollar added 0.2 percent to 111.43 yen.

Toyota Motor Corp edged up 0.4 percent, Nissan Motor Co fell 0.2 percent, while Panasonic Corp shed 0.1 percent.

The mining sector outperformed the market as oil prices rose, supported by reports that an OPEC-led supply cut would not only be extended into next year but might also be deepened to tighten the market and further prop up prices.

Inpex Corp soared 1.4 percent and Japan Petroleum Exploration Co gained 0.6 percent.

The broader Topix added 0.4 percent to 1,565.76 and the JPX-Nikkei Index 400 advanced 0.4 percent to 13,988.42. (Reporting by Ayai Tomisawa; Editing by Eric Meijer)