[You must be registered and logged in to see this link.]The 38-year-old victim also had a stab wound to his neck and was pronounced dead an hour later in hospital.
Two female passengers in their 20s were also injured in the neck and other parts of their bodies, though their conditions were not life-threatening.
Japanese television footage showed other passengers desperately trying to escape to other cars of the Osaka-bound train.
Witnesses said passengers were in tears as they attempted to flee in panic. "All of a sudden, a lot of passengers were dashing... people panicked," one male passenger told the Japanese newspaper Mainichi Shimbun.
The Nozomi train made an emergency stop at Odawara station, just west of Tokyo, following reports of a knife-wielding attacker on board.
Officers apprehended Kojima in the carriage. He was pictured cuffed with blood covering his hands and face as he was arrested.
Odawara police official Satoshi Oiye said the suspect admitted he had attacked the passengers. Police are continuing to investigate his motives, Mr Oiye added.
Japanese media reported that Kojima said he made the assaults because he was 'irritated and felt like attacking anyone'.
Mr Oiye said investigators also found a machete believed to be Komaji's at the stabbing scene. It is understood he intended to use it in further attacks on the train.
A relative who lived with Kojima said the suspect had sounded suicidal.
“He was a quiet and gentle type,” the relative in his 50s told The Asahi Shimbun. “He had said things like, ‘I cannot see any meaning in my life. I will die,’ but I never dreamed he would commit [such a crime].”