Police said Saturday they had arrested a 73-year-old man for confining his mentally ill son to a cage in Hyogo Prefecture for more than 20 years.

Yoshitane Yamasaki, suspected of confining his 42-year-old son in a wooden cage inside a prefabricated hut next to his house in the city of Sanda, was quoted by investigative sources as saying that he began confining his son when he was 16 years old as his illness made him act violently.

As of now, police have arrested the father for confining his son for a 36-hour period from 10 a.m. on Jan. 18. The timing is apparently related to when authorities learned of the son's confinement when a city official visited the home in connection with nursing care for Yamasaki's late wife.

Yamasaki bathed his son and provided him food every other day, according to investigative sources, who said the son does not appear to have any serious health problems.

The cage was about 1 meter high, 90 cm long and 1.8 meters wide, the sources said.

A plastic sheet had been placed on the floor beneath the cage in which the son was confined, and the prefabricated hut was equipped with an air conditioner, police said.

In December in Osaka Prefecture, police arrested a couple for confining their 33-year-old daughter in a tiny room for 15 years.

An autopsy found that the woman, who weighed a mere 19 kg, had frozen to death in the room, which had no heating.