TOKYO, Oct 22 (Reuters) - Japanese shares ended weaker on Thursday, as a firmer yen threatened earnings of exporters and amid fears that agreement on a key U.S. stimulus bill will not be reached until after the presidential election on Nov. 3.

The Nikkei 225 Index ended down 0.70% at 23,474.27, while the broader Topix fell 1.09% to 1,619.79.

The yen jumped to a one-month high against the dollar on Wednesday as investors grew more concerned about stalled negotiations over a new round of U.S. fiscal stimulus.

Some traders are also reducing their exposure to riskier assets ahead of the U.S. elections, which could cap gains in Japanese shares. Rising COVID-19 cases in Europe and the United States also hurt sentiment.

"There are a lot of people waiting to buy stocks on the dip," said Ayako Sera, market strategist at Sumitomo Mitsui Trust Bank.

"At the same time, the upside is limited because there is still uncertainty in the market about the election and the coronavirus."

The underperformers among the Topix 30 were Central Japan Railway Co down 3.35%, followed by East Japan Railway Co losing 3.08%.

Shares of ANA Holdings Inc ended down 4.08%. The airline hit its lowest level in more than two months after media reports that ANA will book a record net loss as the pandemic devastates global travel demand.

Weighed down partly by a stronger yen, Toyota Motor Co fell 0.61%, Honda Motor lost 1.93% and Sony Corp slid 0.98%.

The stocks that gained the most among the top 30 core Topix names were industrial robot maker Fanuc Corp up 0.26 %, followed by Japan Tobacco Inc rising 0.05%.

There were 40 advancers in the Nikkei index against 180 decliners

The volume of shares traded on the Tokyo Stock Exchange's main board was 0.73 billion, compared with the average of 1.09 billion in the past 30 days. (Reporting by Stanley White; Editing by Aditya Soni and Sherry Jacob-Phillips)