The bodies of five people were found after a blaze gutted a restaurant and residence early Saturday in Oyama, Tochigi Prefecture, police said.
The blaze broke out at around 1:15 a.m. and was extinguished about three hours later.
The police said they were unable to contact owner Kazumi Tanaka, 58, his father Shioya, 87, his wife Michiyo, 60, daughter Chika, 30, and granddaughter Hina, 9.
The police believe the bodies are those of the family members and are continuing the identification process.
Six people lived in the house, but Tanaka's second son, 23, was away for work when the fire occurred.
According to an investigative source, the fire is believed to have started in the kitchen.