The 225-issue Asian benchmark stock average, aided by the yen's decline against the U.S. dollar, which helps boost Japanese exports, had risen 1.38 percent or 209 points from its Friday close early Monday to more than 15,347 points, a level not seen since December 2007.
Investors were encouraged by the U.S. dollar continuing to trade at more than 102 yen as well as expectations of higher corporate earnings and optimistic U.S. economic data.
Nikkei.com reported the higher dollar triggered more buying of Japanese car stocks and other blue-chip Japanese exporters.
The Nikkei had crossed the 15,000 point level last Wednesday. A lower yen, besides making Japanese exports cheaper, also helps push Japan's inflation higher, which is needed to lift the country's export-dependent economy out of its years of deflation or falling prices.
The government of Prime Minister Shinzo Abe has made its top priority to end deflation. The Japanese economy is the third-largest in the world behind the United States and China.
The government and the Japanese central bank have introduced numerous stimulus measures for an economic recovery. Last January, the Bank of Japan doubled its inflation target to 2 percent.
Some analysts have said the yen could dip to 105 against the U.S. dollar as central banks in many countries cut interest rates, which in turn create demand for dollars.
Separately Monday, Japan's Cabinet Office in its May monthly economic assessment report gave a positive signal, saying the economy "is picking up slowly," which was better than its April assessment of the economy "showing movements of picking up recently, while weakness can be seen in some areas."