Japan on Tuesday executed a man convicted of killing seven people in a truck ramming and stabbing rampage in Tokyo's popular Akihabara electronics district in 2008, the justice ministry said.

Justice Minister Yoshihisa Furukawa said Tomohiro Kato had undertaken "meticulous preparation" for the attack and displayed a "strong intent to kill".

Furukawa said he "approved the execution after extremely thorough scrutiny," noting that Kato's death sentence had been upheld by the court system.

Kato went on the rampage on June 8, 2008, telling police: "I came to Akihabara to kill people. It didn't matter who I'd kill."

He was arrested on the spot shortly after the attacks, in which he rammed a rented two-tonne truck into a crowd of pedestrians before getting out and randomly stabbing people.

"This is a very painful case that led to extremely grave consequences and shocked society," Furukawa said on Tuesday.

Police said Kato documented his deadly journey to Akihabara on internet bulletin boards, typing messages on a mobile phone from behind the wheel of the truck and complaining of his unstable job and his loneliness.

Prosecutors said his self-confidence plummeted after a woman he chatted with online abruptly stopped emailing him when he sent her a photograph of himself.

His anger against the general public grew when his comments on an internet forum, including his plans to go on a killing spree, were met with no reaction at all, prosecutors said.

While awaiting trial, Kato wrote to a 56-year-old taxi driver whom he injured in the stabbing spree, expressing his remorse.

The victims "were enjoying their lives, and they had dreams, bright futures, warm families, lovers, friends and colleagues," Kato wrote according to a copy published in the Shukan Asahi weekly.

And in court, he offered remorse for the attack.

"Please let me use this occasion to apologise," he said about the bloody rampage that also left 10 people injured. (AFP)