A 23-year-old riot police officer was found dead Saturday afternoon after apparently shooting himself at the Takahama nuclear power plant in Fukui Prefecture, police said.

The officer apparently died instantly after shooting himself in the head at a water-treatment building for the No. 2 and No. 3 reactors of the plant, operated by Kansai Electric Power Co., the police said.

The officer had been assigned to the Takahama nuclear plant as a guard by the Osaka Prefectural Police since Aug. 6.

He went missing at 2:20 p.m. after having worked earlier in the day. A colleague found him dead at about 4 p.m., the police said.

A note addressed to his family was found, the Osaka police said, adding they are investigating his reason for committing suicide.

The water-treatment building, where the body was found, is designed to send high-temperature and high-pressure water into the reactors' steam generators.