A suspect, said to be 25-year-old Tomohiro Kato, has been arrested near the scene.
The stabbing came on the anniversary of a 2001 knife attack which killed eight children at a primary school.
A police spokesman, Jiro Akaogi, confirmed Mr Kato's identity and arrest.
"The suspect told police that he came to Akihabara to kill people," Mr Akaogi told reporters.
"He said he was tired of life. He said he was sick of everything," he added.
The dead include six men, ranging in age from 19 to 74, and a 21-year-old woman, Kyodo News said.
Reports say the suspect drove a rented truck into a crowd in the early afternoon and then began stabbing people at random.
--- BBC News
Don't understand why the heck anyone would want to go around stabbing people just because he's 'sick and tired'. If you want to be really capable of destroying the world and bringing them to hell with you, go and devise some other more intelligent way. This is such a pervertic crime.