Some experts also question whether monetary policy alone can end deflation in Japan. The country has other deflationary pressures like an aging and shrinking population and cumbersome regulations that make the economy inefficient. They say that lending has not increased at a high enough rate despite the easy money already available because businesses and consumers see little potential for growth.

Mr. Kuroda said that such risks or doubts should not hold the bank back from fighting deflation.

“We have debated the side effects but we are currently not concerned that long-term interest rates might spike, or conversely, that there would be an asset bubble,” Mr. Kuroda said. “That risks exist should not hold us back from pursuing much-needed monetary easing. We will keep in mind those risks, but push ahead,” he said.

He also said that once Japan had fought off deflation and restarted its economy, lending would surely follow, spurring more economic growth in a virtuous cycle. “We are already seeing an improvement in sentiment among consumers and companies,” he said. “As the economy expands, and prices rise, lending will also grow.”

In a statement detailing the new measures, the bank said it would buy longer-term government bonds, lengthening the average maturity of its holdings to seven years from three years and expanding Japan’s monetary base to 270 trillion yen by March 2015.

Under that plan, the bank will buy about 7 trillion yen in bonds each month, equivalent to over 1 percent of its gross domestic product, which is almost twice the bond purchases of the United States Federal Reserve Bank.

The policies are part of a new asset purchase framework that focuses on the monetary base instead of the overnight interest rate. That rate has remained close to zero for years with little effect on increasing prices or expanding the economy. The bank will also consolidate all its purchases in a single operation in an effort to improve transparency of the bank’s purchases.

Mr. Kuroda said that the bank would suspend, for now, a long-standing rule that limits its bond holdings to the amount of money in circulation. The new governor pointed out that limit had already been surpassed anyway.