According to public broadcaster NHK, Yoshitane Yamasaki, 73, said he locked up his son, now 42, because he suffered from mental problems and was sometimes violent, reports the BBC.
The cage, 1 metre in height and less than 2 metres in width, was in a hut next to Yamasaki's house in Sanda city.
The son, who now suffers a bent back, is being looked after by authorities.
A visit by a city official to Yamasaki's home in January alerted authorities to the man's confinement.
Investigators believe Yamasaki began confining his mentally ill son from the age of 16 when he began to "act up".
Yamasaki has reportedly admitted the allegations, telling authorities that he fed his son every day and also allowed him to bathe.
(This story has not been edited by Social News XYZ staff and is auto-generated from a syndicated feed.)
