By the midday break, the Nikkei climbed 1.1 percent at 9,319.36, trading above the 9,300-line for the first time since May 2. The broader Topix advanced 0.9 percent to 773.88, the highest level since July 6.
But with U.S. markets closed for the Thanksgiving holiday on Thursday and the Japanese market closed on Friday for Labor Day, volumes may stay low and gains could be trimmed in late trade, market analysts said.
They noted that investor sentiment remains upbeat, but markets are closely watching talks among U.S policymakers on how to avoid the U.S. "fiscal cliff," which has raised fears about the direction of the world's largest economy.
"A lot of investors have positions to unwind when the Nikkei reaches 9,400," said Yutaka Miura, senior technical analyst at Mizuho Securities. "Until there is a clear sign that the U.S. fiscal cliff is resolved, the Nikkei's upside will likely be capped around this level as major Japanese stocks are highly sensitive to the health of the U.S. economy."
Among other exporters, Advantest Corp surged 2.8 percent to 1,069 yen, Nikon Corp added 3.8 percent to 2,176 yen and Tokyo Electron Ltd gained 1.8 percent to 3,595 yen.