The Tokyo Fire Department says 17 passengers were injured, including three seriously. Not all of them were stabbed and most of the other injuries were not serious, the fire department said.
The attacker, whom police identified as 24-year-old Kyota Hattori, was arrested on the spot after Sunday's attack and was being investigated on suspicion of attempted murder, the Tokyo metropolitan police department said on Monday.
The attacker, riding an express train headed to Tokyo's Shinjuku station, abruptly took out a knife and stabbed a seated passenger - a man in his 70s - in the right chest, police said.
Injury details of other 16 passengers are still being investigated.
Police said he told authorities he wanted to kill people and get the death penalty. Nippon Television said he also said he used an earlier train stabbing case as an example.
Witnesses told police the attacker was wearing a bright outfit - a green shirt, a blue suit and a purple coat - like the Joker villain in Batman comics or someone going to a Halloween event, according to media reports.
A video posted by a witness on social media showed the suspect seated, with his leg crossed and smoking in one of the train cars, presumably after the attack.
Tokyo police officials said the attack happened inside the Keio train near the Kokuryo station.
NHK said the suspect, after stabbing passengers, poured a liquid resembling oil from a plastic bottle and set fire, which partially burned seats.
The attack was the second involving a knife on a Tokyo train in three months.
In August, the day before the Tokyo Olympics closing ceremony, a 36-year-old man stabbed 10 passengers on a commuter train in Tokyo in a random burst of violence.
The suspect later told police that he wanted to attack women who looked happy.
