Atsushi Aoki was fishing in the mountains of the Gunma Prefecture region when the animal emerged from woodland.
The snarling black bear – reportedly standing at 6ft 3ins on its hind legs – set upon him in an unprovoked attack, he told Japanese broadcaster TBS.
However, Mr Aoki said he was more than a match for his assailant, fighting the animal off with his bare hands.
Despite being knocked to the floor, he managed to pick himself up and face up to his opponent.
Rather than fleeing, he used his own deadly fighting skills to take the upper hand, punching the bear between the eyes.
The animal then retreated.
Mr Aoki told reporters the bear stood over him with “an imposing stance”.
The fisherman was quoted in Singapore newspaper The Straits Times saying: “It came pouncing towards me when my eyes met the bear’s.
“Its rounded ears were perfectly circular just like a teddy bear’s and its face was so huge.
“The bear had such, such great strength. I was knocked over when it leapt at me. It scratched me and bit me. But in the end I managed to trick the bear, poked it in the eyes and it ran away.”
After the attack, Mr Aoki apparently made his own way to a nearby hospital in Naganohara town, where he received treatment for minor injuries.
He sustained bite and claw marks on the right side of his upper body, head and arms, and an injury to his leg, but was otherwise unharmed.