Industry Minister Banri Kaieda put on full protective gear for a 45-minute visit during which he thanked workers.
Workers are engaged in a release of radioactive water into the sea and are pumping nitrogen to prevent explosions.
A top executive of plant operator Tepco has now publicly apologised for the “worries and troubles” it has caused.
The earthquake and tsunami on 11 March killed more than 12,800 people. Nearly 15,000 are listed as missing. Hundreds of thousands of people have been made homeless and a number of communities in Japan’s north-east have been devastated.
Full text and video footage at “Japan: Minister in first tour of stricken nuclear plant”.