* SoftBank jumps to 17-year high
* Universal Entertainment tumbles as chairman accused of improper loan
By Ayai Tomisawa
TOKYO, June 9 (Reuters) - Japan's Nikkei soared on Friday as index-heavyweight SoftBank leapt 7 percent after its unit agreed to buy a robotics firm, but traders said chances of a shock election result in the UK, where the vote was underway, had put investors on edge.
The Nikkei share average, built on early gains to stand 0.8 percent higher at 20,065.89 points by midmorning. For the week, the index is poised to post a 0.5 percent drop.
Trading was volatile after a UK election exit poll pointed to a hung parliament, a shock result that would plunge British politics into turmoil and could delay Brexit talks.
"If that's the case, there will be big uncertainty over Brexit talks thus the market will likely become risk averse," said Norihiro Fujito, a senior investment strategist at Mitsubishi UFJ Morgan Stanley Securities.
With the count still underway, the BBC said that Prime Minister Theresa May's Conservative party was forecast to remain the largest party in parliament, predicting that the Conservatives would lose fewer seats than the exit poll had suggested, but would still come up short of a majority.
The chance that the Conservatives could scrape majority, however, was enough to spark short-covering by short term investors such as hedge funds and commodity trading advisors, traders said.
Meanwhile, SoftBank Group Corp jumped more than 7 percent to hit a 17-year high after a subsidiary of the company had agreed to buy robotics firm Boston Dynamics from Alphabet Inc.
SoftBank contributed a hefty 74 positive points to the Nikkei benchmark index, which was why the index was outperforming the broader Topix, which was only up 0.3 percent.
Traders said that overnight gains in Nvidia Corp and Alibaba also contributed to gains in SoftBank, which has a stake in them.
Exporters were mixed, with Toyota Motor Corp rising 0.7 percent, Nissan Motor Co falling 0.1 percent and Panasonic Corp declining 1.1 percent.
Fujifilm Holdings stumbled more than 4 percent after the Nikkei reported that the company's accounting irregularities spread to its Australian unit.
Also underperforming the market was slot machine maker Universal Entertainment Corp, which plunged as much as 13 percent after the company said it was investigating what it suspects was an improper transfer of funds by its chairman to a company he controls. (Editing by Simon Cameron-Moore)