A spokeswoman for Japan's Tokyo Electric Power Company said Monday that the director of the troubled Fukushima Daiichi nuclear power plant is stepping down for health reasons.

Chie Hosoda said 56-year-old Masao Yoshida has been hospitalized for treatment of an unspecified illness and will be relieved of his post Thursday.

She added that details of his illness could not be given to protect Yoshida's privacy, declining to say whether his illness was related to radiation exposure.

Yoshida is being replaced by Takeshi Takahashi, who was in charge of nuclear power plant operations at TEPCO's head office in Tokyo.

Japan's Fukushima nuclear power plant was crippled by a massive quake and ensuing tsunami that struck in March. Tens of thousands of people were forced to flee their homes due to leaking radiation.

Many Japanese consider Yoshida a hero for defying orders not to flood the crippled Fukushima-1 reactors with seawater, thus preventing what could have been a much larger radiation disaster.

The plant director was also one of the first TEPCO managers to offer what was seen as a sincere apology for the crisis.

Yoshida had pledged that the crippled reactors would be brought to a stable condition of cold shutdown by the end of this year.