Four or five men broke into a house in Tokyo's Adachi Ward early Sunday and stole about 100 million yen in cash after tying up the owner, his wife and daughter, police said.
The men entered the house around 4 a.m. and threatened Mitsuo Komiya, a 51-year-old company manager, with a stun gun, demanding, "Money, money." They forced him to open a safe and took the money, the police said.
Komiya told the police that the men may have been foreigners.
The victims' hands and legs were bound with clothing. The three managed to free themselves and notify the police after the group fled. None of them was hurt.
The police said two of the robbers appeared to be around 40 years old and another around 30. At least these three were wearing masks.
Police believe the group entered through a window that was found broken on the ground floor of the two-story house. Five people live in Komiya's house, but the other two were out at the time of the incident.