The TOPIX index, which covers all first-section shares on the Tokyo Stock Exchange, added 1.14 points or 0.1 percent to 1,130.06, its highest close since August 2.
It has gained 45 points or 4.2 percent in the last eight days after tumbling to a three-month low on August 16. Analysts said the market was finding solid support now that oil prices had retreated. US light crude was at $43.62 a barrel in Asian trade, against last Friday's record high of $49.40.
"The recent fall in oil prices is prompting buy-backs in stocks like exporters that were hit hard in selling prompted by the oil jitters," said Teruhisa Ishikawa, manager of the investment information department at Mizuho Investors Securities.
"The market could find it difficult to rise further from the current level unless oil prices fall below $40, but investors would also find it hard to sell too many shares, given strong fundamentals here."
The benchmark Nikkei average moved in and out of positive territory throughout the day, ending flat at 11,129.33, down 0.69 point or 0.01 percent.
It had gained 240 points in the previous three sessions, ending at a three-week high on Wednesday, and went as high as 11,225.95 on Thursday.
Trading was active, with 1.433 billion shares changing hands on the first section, the highest total since June 11 and up from 1.283 billion on Wednesday.
Gainers outnumbered decliners 721 to 656.
The rise in turnover, plus the Nikkei's recovery above chart resistance at 11,000, helped top brokerage Nomura Holdings Inc and its rivals.
Nomura rose 0.66 percent to 1,520 yen and smaller rival Daiwa Securities Group Inc climbed 2.22 percent to 738 yen.
Before the opening, government data showed Japan's trade surplus in July rose 44.2 percent from a year earlier to 1.1378 trillion yen ($10.33 billion), beating the market consensus and underlining views that exports are holding up.
Optimism is also rising that Japan will revise up its April-June gross domestic product (GDP) figures after capital spending data are unveiled in September.
Toyota Motor Corp, Japan's largest auto maker, climbed 2.08 percent to 4,410 yen and smaller rival Honda Motor Co Ltd advanced 0.74 percent to 5,420 yen as a fall in oil prices eased worries about the global economic outlook.
But Toshiba Corp, Japan's second-largest electronics conglomerate, fell 0.97 percent to 410 yen after gaining 2.2 percent in the past two days and consumer electronics giant Sony Corp was down 0.78 percent at 3,830 yen.
Profit-taking also hit Kawasaki Kisen Kaisha Ltd, Japan's third-largest shipping firm, whose shares fell 0.88 percent to 678 yen after touching a 14-year intraday high of 697 yen.