The 12-year-old was skateboarding with two friends on Wednesday when they came across the circus, which was in the process of being set up, reported newspaper Ouest-France.
The boy approached one of the cages, which contained a lion and two Bengal tigers.
He stood on a barrier surrounding the cage and gripped one of the bars of the cage to steady himself and get a closer look at the animals.
Too close for comfort for one of the tigers, which decided to try to take a chunk out of the boy's left hand.
The boy was rushed to hospital where his injuries were not too serious.
There was little sympathy on offer, with even the boy's mother saying she wouldn't be making an official complaint.
"He was actually quite lucky," said police, "even if he was really foolish."