A gear housing for an electric power steering device has a front-side housing and a rear-side housing. The front-side housing has a worm wheel housing portion, a worm housing portion, and reinforcing ribs. The worm wheel housing portion has a worm wheel cylindrical portion and a ring shaped worm wheel bottom portion bent inward in a radial direction from a front end portion of the worm wheel cylindrical portion. The worm housing portion is provided on a part in a circumferential direction of an outer-diameter side portion of the worm wheel housing portion. The reinforcing ribs are provided on a front side surface of the front-side housing, extend in a direction in which an engagement reaction force acts between the worm wheel and a worm of the worm shaft, and span between the worm housing portion and the worm wheel bottom portion.