The benchmark Nikkei 225 stock index climbed as much as 4.7 percent to 13,225.62, its highest level in nearly five years, and closed up 1.58 percent, or 199.10 points, at 12,833.64.
The Topix index of all first-section shares climbed 4.15 percent, or 43.02 points, to 1,080.78.
Shares were boosted by a tumbling yen, which sank to a three-and-a-half year low against the dollar.
The Bank of Japan said on Thursday it would boost its asset purchases, including Japanese government bonds, while pledging to meet a two percent inflation target within two years, aimed at reversing decades of falling prices.
The BoJ said it would “enter a new phase of monetary easing both in terms of quantity and quality”.
Among its purchases would be exchange-traded funds and longer-term bonds, with the latter aimed at pushing down long-term interest rates to encourage companies and individuals to borrow.
Japan’s economy has been battling more than a decade of falling prices.
New governor Haruhiko Kuroda had previously said he would do “whatever it takes” to drive growth.
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