Tokyo's benchmark stock index has risen above 30,000 for the first time in over a year and a half.
The Nikkei 225 Stock Average gained more than 0.5 percent in Wednesday morning trading from the previous day's close.
The Nikkei average's upward trend began last month as demand from foreign investors drove stock prices higher.
Robust earnings and improved profit outlooks for Japanese companies are drawing buyers, including those based outside the country.
Slowing economic growth overseas amid interest-rate hikes in the United States and Europe is also making Japanese stocks more attractive.