The deadly lunchtime assault paralyzed the Akihabara neighborhood, which is wildly popular among the country's cyber-wise youth. The killings were the latest in a series of grisly knifings that have stoked fears of rising crime in Japan.
A 25-year-old man, Tomohiro Kato, was apprehended in the attack. Local news reports initially said the man was a self-proclaimed mobster, but national broadcaster NHK later said the suspect was not a gang member.
"The suspect told police that he came to Akihabara to kill people," said Jiro Akaogi, a spokesman for the Tokyo Metropolitan Police Department.
"He said he was tired of life. He said he was sick of everything," Akaogi said.
The violence began when he crashed a rented, two-ton truck into pedestrians. News reports said he jumped out and began stabbing the people he'd knocked down with the truck, then turned on horrified onlookers.
Police confirmed seven deaths - six men and one woman - but they could not say whether the victims had died of injuries from the truck or were stabbed to death.
Reports said the attacker grunted and roared as he slashed and stabbed at Sunday shoppers crowding a street lined with huge stores packed with computers and other advanced electronics, and the latest in video and computer games.
"He was screaming as he was stabbing people at random," an unidentified witness told NHK.
The attack paralyzed the district and sent thousands of Sunday shoppers into a panic. At least 17 ambulances rushed to the scene, and TV footage showed rescue workers tending to victims in the street.
An unidentified witness told NHK the suspect dropped the knife after police threatened to shoot him. An amateur video filmed by a mobile phone showed policemen overpowering the bespectacled suspect.
Another amateur video taken five minutes after the rampage showed shoppers helping the victims and a man screaming, "Ambulance, Ambulance!" according to NHK.
Police earlier said 12 people were wounded but later lowered the number 10.
Once rare, stabbing attacks have become more frequent in Japan in recent years as violent crime has increased.
In March, one person was stabbed to death and at least seven others were hurt by a man who went on a slashing spree with two knives outside a shopping mall in eastern Japan. In one of the worst attacks, a man with a history of mental illness burst into an elementary school in Japan in 2001 and killed eight children. The killer was executed in 2004.