The late Prime Minister Keizo Obuchi left behind some 600 million yen in taxable assets when he died in May at the age of 62, a Gunma Prefecture tax office said Friday.

The amount is more than five times the 115 million yen appearing in the last voluntary disclosure of his assets, filed in November 1999.

that he had around 115 million yen in assets as of Oct. 5 that year, the day he formed his last Cabinet.

There were no major differences in the assets between the two dates.

The substantial increase apparently stemmed from a revaluation of stockholdings and properties using gauges to bring them in line with market values in an attempt to impose inheritance taxes.

For voluntary disclosure, Cabinet ministers are allowed to declare the amount of their stockholdings at par value, rather than market value, while the value of their properties is computed by using yardsticks to measure the fixed asset tax.

The yardsticks tend to value properties more conservatively than inheritance tax gauges.

The marked difference between the two values, however, is likely to raise further questions over the validity of asset disclosures by Cabinet ministers.

Obuchi's assets have been passed on to four people, including his widow, Chizuko, and their second daughter, Yuko, who was elected to the House of Representatives last June from her father's constituency in Gunma.

Sources close to the family said the assets include Obuchi's home in Tokyo's Kita Ward as well as properties in Fukushima Prefecture, deposits, stocks and memberships of eight golf courses.

Chizuko owes no inheritance taxes thanks to deductions allowed for a spouse, while Yuko and two others owe a total of 75 million yen in such taxes, the sources said.

Obuchi died last May 14, six weeks after falling into a coma following a stroke.