A teenage boy armed with a knife entered a junior high school in Gifu Prefecture on Thursday and threatened to jump from a ledge above the third floor.
He reportedly issued no specific requests and merely stood quietly on the ledge in question, school officials said.
Police and officials at Honjo Junior High School in the city of Gifu eventually persuaded the boy to come down; he was detained at around 3:25 p.m., about 90 minutes after he entered the school. He was arrested for intruding onto the premises and violating laws controlling firearms and swords.
The city fire department said the boy, a carpenter's apprentice, graduated from the school in March. He threatened to jump to his death, they added.
The school dismissed classes and ordered its 500 students to leave immediately, the officials said.
The police received a call from the school around 1:15 p.m. that a boy carrying a knife had entered the school premises and was standing on the 30-cm wide ledge.
The boy had no notable problems when he was a student at the school, and had occasionally visited it to chat with teachers after he graduated, according to school officials.