
The Nikkei gained 258.31 points, or 2.01 per cent, to trade at 13,091.95 at 11:30 am (0230 GMT) at the end of the morning session.
The broader-based Topix index was up 19.72 points, or 1.85 per cent, at 1,085.96.
The central bank was expected to buy a total of 1.2 trillion yen (12.2 billion dollars) in Japanese government bonds with remaining maturities of at least five years early this week, the Nikkei business daily reported Sunday without citing any sources.
New bank governor Haruhiko Kuroda said Thursday that the bank had decided to start aggressive monetary easing measures to achieve a 2-per-cent rate of inflation to pull the world's third-largest economy out of 15 years of deflation.
On currency markets at 11:30 am, the dollar traded at 98.34-38 yen, up from Friday's 5 pm quote of 96.30-32 yen.
The euro was quoted at 127.78-82 yen, up from 124.31-35 yen late Friday, and at 1.2992-2996 dollars, up from 1.2908-2910 dollars.
A weaker yen makes Japanese goods less expensive abroad and improves repatriated earnings.//DPA