The animal was first noticed at 9.40am hopping around near the electronic ticket gates in the Shibuya Station in the middle of the Japanese capital.
Not content with its place by the gates, however, it darted downstairs towards the entrance to another train line before scaling a pillar and flitting between the ticket machines with officials in hot pursuit.
Bored with the game, it climbed onto an information board and dozed for a couple of hours while commuters and railway staff looked on.
Television pictures showed the primate, two-foot tall and brown, sitting tranquilly atop the board and contemplating the watching crowd.
"It's a monkey, it's not like it did anything bad," said a police spokesman.
A little later railway staff and police cleared the area to being their attempt to catch the runaway monkey.
Having surrounded the information board with green netting, they hoped to pounce on the animal as soon as it leapt from its perch.
But when it finally jumped down, it slipped through the police cordon, darted into the crowd and disappeared - apparently out of the station.
"I've heard of mice before, but nothing like this," said a Tokoy Metro spokesman.