A bullet believed to have come from a Self-Defense Forces training ground pierced through the roof of a two-story house in Takashima, Shiga Prefecture, Thursday, police said.

An official of the Ground Self-Defense Force's Okubo Base in Uji, Kyoto Prefecture, said Friday the bullet is believed to have strayed from a machine-gun shooting practice held at the base Thursday. The round found at the house was the same type as the ones used for the training, the official said, adding that the GSDF will set up a task force to investigate the case.

The police said a 6 cm-long bullet, about 1.2 cm in diameter, was found at the house of a 47-year-old company employee. The man's 80-year-old mother reportedly heard a smashing sound on the second floor at round 1 p.m. Thursday. The man's 27-year-old son was at home, too, but no one was injured, according to police.

A hole of 1 or 2 cm was found in the ceiling of a room on the second floor, they said.