A 23-year-old man was arrested late Saturday on suspicion of fatally stabbing his father, brother and grandfather in Tokorozawa, Saitama Prefecture, police said.
The man, who is unemployed, has a history of mental illness, the police said.
After behaving violently during dinner, the man ran out of the house carrying two knives, prompting his 50-year-old father, 20-year-old brother and 72-year-old grandfather to chase after him, police said.
According to investigations, the family began eating dinner at around 9 p.m., after closing up the father's in-house, Japanese-style eatery for the day. However, the elder son suddenly got up and said, "(They're) telling me to kill," grabbed two knives from the restaurant kitchen and started becoming violent.