The headline Nikkei index at the Tokyo Stock Exchange added 27.90 points to end the early session at 9,710.11. The Topix index of all first section shares rose 0.25 percent or 2.09 points to 844.27.
"The earnings season has finally kicked off in Japan, but it's still difficult to pin down a clear market direction," said Toshikazu Horiuchi, an equity strategist at Cosmo Securities.
He expected the Nikkei to remain within a narrow band of 9,650-9,750.
Trading in Tokyo remained quiet, while foreign players kept away from the market after Good Friday.
Global investors were waiting for US Fed Chairman Ben Bernanke's news conference on Wednesday following a policy announcement, he said.
Investor sentiment was lifted by a report that construction equipment maker Komatsu's operating profit surged thanks to robust demand in North America, said Masayoshi Yano, a senior market analyst at Meiwa Securities.
"I have been quite cautious on the (overall) corporate earnings outlook, but it may be slightly stronger than expected," he said.
At the Tokyo bourse, Komatsu rose 0.65 percent to 2,792 yen by the lunch break.
Toyota Motor rose 0.15 percent to 3,300 but Nissan Motor fell 1.42 percent to 762.
Sony eased 0.08 percent to 2,475, while Panasonic was flat at 993.