* No strong concerns over cost of easy policy - BOJ Kuroda

* BOJ will ease if needed to hit price goal - Kuroda

* Japan FinMin Aso warns against excessive pessimism

* Japan firms may shift out of UK due to Brexit - Aso (Adds quotes, detail)

By Leika Kihara

WASHINGTON, Oct 7 (Reuters) - Bank of Japan Governor Haruhiko Kuroda said it was hard to achieve balanced economic growth with monetary policy alone, adding that G20 nations shared the view fiscal and structural policies must also play a key role in boosting growth.

But he shrugged off the view that global policymakers were becoming increasingly concerned about the rising cost of prolonged ultra-loose monetary policies, signalling that central banks still had the ammunition left to stimulate the economy.

"I don't think there was a strong feeling shared among (G20 nations) that monetary policy was reaching its limits or that an over-reliance on monetary policy was causing big problems," he told a news conference on Friday.

Kuroda said he told a finance leaders' meeting of Group of 20 major economies that the BOJ was ready to expand monetary stimulus if necessary to achieve its 2 percent inflation target.

Japanese Finance Minister Taro Aso also warned policymakers against being overly pessimistic about the global economy, even though various risks loomed on the outlook.

"What's important is to identify the root of the problem and take appropriate measures," Aso told the same news conference, pointing to concerns voiced by some policymakers on sluggish global trade.

"If the slowdown in trade is due to broadening protectionist sentiment, that's a cause for concern so policymakers should act to eliminate barriers against free trade," he added.

Aso said some big Japanese companies may decide to shift their European countries out from London to other cities as Britain proceeds toward exiting the European Union.

That may force smaller Japanese firms operating in Britain to follow suit, he said, adding that policymakers in Tokyo may urge domestic banks to ensure they help such firms in funding any such move.

"It's uncertain how (Brexit) will actually unfold but we can say some Japanese firms may shift their headquarters out from London," Aso said.

(Reporting by Leika Kihara; Editing by Sandra Maler)