Matushita is reported to have hanged himself. His wife found Matushita's body and called police. Matushita was taken to the hospital where doctors confirmed he was dead.
Tokyo Metropolitan Police said the circumstances showed no sign of foul play after preliminary investigation and police found something like a suicide note near the body.
Matushita was scheduled to attend a meeting Monday afternoon but he called his colleagues in the morning to say he would be absent.
Matushita, 73, a member of the People's New Party, partner of the ruling Democratic Party, was appointed the ministerial position in the cabinet reshuffle at early June.