Wholesale prices rose 1.4 percent in June from a year earlier for the fourth straight monthly rise, the Bank of Japan said Monday in a preliminary report.
The prices, measured by the central bank's corporate goods price index, registered 96 against the base of 100 for 2000.
The index rose 0.2 percent in March for the first rise since July 2000, and registered gains of 0.6 percent in April and 0.9 percent in May.
The rises have prompted expectations that the economy is finally pulling out of deflation.
The CGPI is designed to show movements of the prices of goods traded among companies.
The margin of gain in June was the biggest since the 1.4 percent increase shown in September 1997, the central bank said.
In June, prices of petroleum and coal products surged 12 percent, contributing largely to the overall wholesale price rise during the month, it said.
The rise in the petroleum and coal category stemmed largely from hikes in crude oil prices in the world market.
Prices of agricultural products rose 7.3 percent, led by gains in pork prices, and steel product prices surged 13.3 percent, led by strong demand from China. But prices of electrical appliances fell 4.1 percent.
Export prices declined 3.4 percent from a year earlier in yen terms, but rose 1.4 percent in terms of contract currencies.
Import prices rose 5.3 percent in yen terms and 11.7 percent in terms of contract currencies.