The Nikkei 225 index at the Tokyo Stock Exchange added 98.36 points to close at 8,883.69.
The Topix index of all first-section issues rose 1.32 percent, or 10.00 points, to 767.40.
The market was underpinned by hopes Greece will strike an agreement with creditors at this weekend's European Union leaders summit, despite an overnight standoff in the troubled country's debt-reduction talks.
A weaker yen against the dollar was seen broadly aiding Japanese stocks.
The dollar stood at 77.92 yen in Tokyo, edging up from 77.71 yen in New York Tuesday.
The euro was mixed at $1.3022 and 101.47 yen, compared with $1.3030 and 101.25 yen in New York.
"Large-caps are gaining attention on the backdrop of the weaker yen," said Okasan Online Securities chief strategist Yoshihiro Ito.
"The ground is firming, preparing the market for a further rise later this week," he told Dow Jones Newswires.
At one point the Nikkei went over the 9,000 mark but it failed to maintain the rise as some players took a wait-and-see stance before the US Federal Reserve finished its policy board meeting later Wednesday.
Exporters continued to gain.
Toyota Motor added 3.01 percent to 2,877 yen as it slightly upgraded its domestic sales projection. Honda Motor also rose 3.82 percent to 2,773 yen, and Nissan firmed 2.50 percent to 739 yen.
High-tech firms that supply parts to Apple rose after the iPhone maker reported stellar quarterly earnings results.
Electronic parts maker Murata Manufacturing rose 2.65 percent to 4,260 yen. Sony soared 4.76 percent to 1,454 yen, Toshiba added 1.78 percent to 344 yen, and Panasonic climbed 2.50 percent to 656 yen.
But iPhone service carriers Softbank and KDDI both slipped, the former dropping 0.50 percent to 2,192 yen and the latter losing 0.62 percent to 481,500 yen.