TOKYO, Jan 20 (Reuters) - Japan's Nikkei share average

advanced on Monday, buoyed by gains on Wall Street and a weaker

yen, even as a potential source of market volatility loomed in

the form of U.S. President-elect Donald Trump's inauguration

later in the day.

The Nikkei gained 1.29% to 38,948.47 as of the

midday recess, starting the week on firm footing after three

straight weeks of declines.

The broader Topix rose 1.36%.

Whether the Nikkei can retain the momentum depends on the

outcome of many big risk events this week - Trump's inauguration

speech and any immediate executive orders coming in on Tuesday

morning in Japan just when markets open.

U.S. earnings season is gathering pace and Japan's own

corporate reporting season begins on Thursday, with chip-making

equipment manufacturer Disco and factory robot maker Fanuc.

The Bank of Japan will end a two-day meeting on Friday and

recent rumblings from the central bank hint strongly at a

quarter-point interest rate hike. However, that outcome too may

depend on how markets digest Trump's first day in office.

Comments from Trump during Tokyo's morning trading on the

day promised nearly 100 executive orders in the first few hours

of his presidency.

"My impression is there's going to be a huge flow on

information right when Japanese markets open tomorrow," said

Kazuo Kamitani, an equities strategist at Nomura Securities.

"The environment for the market now hinges on whatever Trump

has to say."

Kamitani said that while 40,600 is unlikely to be breached

solely on anything Trump does and 37,600 looks like a firm

floor, "within that range there's likely to be a high degree of

volatility."

Of the Nikkei's 225 components, 198 climbed, 25 fell and two

were flat.

Automakers were the top performers among the

Tokyo Stock Exchange's 33 industry groups, after the yen dropped

0.8% against the U.S. dollar on Friday.

Toyota ( TM ) was up 3.3%. Subaru advanced 3.8%.

The Nikkei's biggest percentage gainer was Daiichi Sankyo ( DSKYF )

, which soared more than 9% after the U.S. Food and Drug

Administration approved a breast cancer treatment it is

developing with AstraZeneca ( AZN ).