A wild boar injured four people Sunday as they walked on a crowded trail outside of Hikone Castle in Shiga Prefecture.
A 78-year-old man was seriously injured, with his ring finger becoming necrotic, and three other people were bitten.
After attacking the people on a trail crowded with tourists, the animal ran to a nearby river and was shot to death by a local hunting group.
Police in Hikone said the female boar was 1.4 meters long and probably weighed about 100 kg.
The animal charged a 74-year-old man from Aichi Prefecture from behind and bit his head. It also bit both the hand and ankle of a 38-year-old man and 54-year-old male care worker, both from Shiga Prefecture.
Boars are not known to live in that location, so it appears the animal either swam across a river or Lake Biwa, Japan's biggest lake, from another area.