The president of Tokyo Electric Power Co., which operates Japan's stricken Fukushima Daiichi nuclear plant, was admitted to hospital last evening, local media reported on Wednesday.
TEPCO president Masataka Shimizu, 66, was suffering high blood pressure and dizziness, public broadcaster NHK said.
A massive earthquake and tsunami on March 11 knocked out the cooling systems of the plant's six reactors --triggering explosions and fires, releasing radiation and sparking global fears of a widening disaster.
On Monday, TEPCO said Shimizu fell sick during the crisis and took several days off from the joint task force that had been set up by the government and the company.
The Mainichi daily had quoted a senior TEPCO official as saying Shimizu had been so sick that he had stayed "mostly in bed" in a separate room in the building where the task force was meeting.
Shimizu has not appeared in public since attending a press conference on March 13, leading to criticism from local media.