Ursus thibetanus japonicus reach a maximum size of around 120 KG while Ursus arctos horribilis reaches a size of 360 KG (individuals of the Kodiak subspecies have been reported to weigh up to 680 KG). Ursus americanus (the kind of bear we have around my house) reach about 250 KG.
Japanese bears do get big, but nowhere near as big as a Grizzly, or even an American Black Bear.
We have Ursus arctos lasiotus (Ussuri bown bears). The maneater was one of those. They definitly reach the size of a grizzly, afterall they are the ancestors of grizzly. They grow even larger than their Kamchatka cousins. Kesagake had a weight of 380 Kg.