Japan's factory output dropped marginally in July, marking the third successive month of decline, the government said in a report on Friday.

According to the Ministry of Economy, Trade and Industry, industrial output here declined 0.1 percent in July, following a 1.8 percent drop a month earlier.

The ministry also said in its preliminary report that the seasonally adjusted index of output at factories and mines stood at 102.4 against the base of 100 for 2010 and changed its assessment of output saying it is "picking up slowly but some weakness can be seen."

This is compared to the ministry's previous assessment that output was "picking up slowly."

The index of industrial shipments in July fell 1.9 percent to 99.9. Inventories, meanwhile, were down 0.2 percent to 111.2 in the recording period, the ministry said.

Manufacturers surveyed by the ministry said that looking ahead they expect factory output to rise 5.6 percent in August and 0.5 percent in September.