Taro Aso, a right-winger seen as a strong contender to become the next prime minister, made the comment when talking about the advantages of exporting Japanese rice to an audience in Toyama prefecture, northwest of Tokyo.

"Ordinary rice is sold at about 16,000 yen a bag here," he said in a speech. "But it is 78,000 yen in China. Even someone with Alzheimer's can see which of 16,000 and 78,000 is the more expensive."

Alzheimer's, an incurable brain disease, occurs mostly in the elderly. Japan has the world's largest percentage of elderly people, with one in five people aged over 65 in 2005.

Aso said on Friday that his remarks had been inappropriate.

"On this, I retract the comments and I want to apologise to those who've been offended," he told reporters.

Prime Minister Shinzo Abe's unpopular cabinet faces its first ballot box test in just over a week. Support for the ruling coalition has been falling due to a string of scandals and verbal blunders.

Earlier this month Defence Minister Fumio Kyuma resigned after making comments seen as justifying the United States' 1945 atomic attacks on Japan.

Health Minister Hakuo Yanagisawa barely held on to his post after referring to women as "birth-giving machines" in a January speech.

Aso himself stirred controversy in 2001 by saying he hoped to make Japan the kind of country where "rich Jews" would want to live and again in March by saying blond, blue-eyed people could not be as successful at Middle East diplomacy as those with "yellow faces."