69 percent in morning deals on Monday, lifted by a rebound on overseas markets after the US central bank on Friday cut a key interest rate to ease a credit squeeze, dealers said.
The Tokyo Stock Exchange's benchmark Nikkei-225 index of leading shares rose 562.89 points to 15,836.57 by the lunch break.
On Friday the index had plunged by 874.81 points or 5.42 percent to a one-year low -- the biggest one-day point drop since April 2000.
The broader Topix index climbed 53.89 yen or 3.6 percent to 1,534.28.
Gainers outnumbered decliners 1,407 to 255, with 56 issues unchanged.
Turnover dipped to 1.04 billion shares from 1.1 billion Friday morning.
US and European stocks rebounded Friday after the US Federal Reserve slashed the lending rate it charges commercial banks to try to calm a recent storm on world financial markets sparked by fears of a credit crunch following problems in the US sub-prime mortgage market.
The central bank cut the rate it charges commercial banks to 5.75 percent, saying it wanted to restore order in financial markets.
The move raised expectations that the Fed may also lower its key federal funds rate -- the overnight rate ban