The Nikkei rose 547.86 points, or 6.4 percent, to 9,153.01. The index had shed more than 1,600 points, or 16 percent, Monday and Tuesday as worries over the nuclear crisis triggered widespread selling.
The plunge prompted Tokyo Stock Exchange President Atsushi Saito to release a statement late Tuesday urging for calm. He noted that the foreign media remained impressed by the potential power of the Japanese economy, and that foreign investors were net buyers the last two days.
"I also believe that Japan's experience, knowledge and technologies in the area of recovering from earthquakes should not be underestimated and that the stock market will calm down soon," Saito said.
Meanwhile, the central bank pumped money into financial markets for a third day.
The Bank of Japan injected 3.5 trillion yen ($43 billion), following injections totaling 23 trillion yen ($283 billion) over the past two days.
Among the day's major gainers were Japan's big exporters. Toyota Motor Corp. rose 8.7 percent, and Sony Corp. shot up more than 10 percent.
Still, investors still kept a close watch on a rapidly changing crisis at a crippled nuclear power plant in northeast Japan. Authorities were still struggling to control the situation at the Fukushima Dai-ichi plant after a string of explosions and fires, as well as a burst of radiation.
Markets elsewhere in the region advanced. South Korea's Kospi added 2 percent to 1,960.94, and Australia's S&P/ASX 200 rose 1.1 percent to 4,580.4. Benchmarks in Taiwan, Singapore and New Zealand were also higher.
For emergency information, assistance, and locating family in connection with earthquake in Japan: http://www.facebook.com/l/6b2e3a9CLMNbUwBsOw1jOL8d5aw/www.jhelp.com
Phone numbers in US and Japan:
202 559 4683
800 373 1110
0570 000 911
011 81 90 7170 4769
011 81 90 3080 6711