A power transmission device includes a drive shaft, one end of which extends beyond a drive-side transmission case, a drive wheel mounted onto the one end of the drive shaft, a driven wheel journaled by a driven-side transmission case that is mounted onto the driven-side transmission case, and a cover member. The cover member is mounted on the driven-side transmission case and covers one end of the drive shaft, the drive wheel and the driven wheel from a location on an outer side of the transmission case. A regulating member is provided to regulate movement of the drive wheel in an axial direction relative to the driven-side transmission case. The regulating member and the cover member are each in separate abutment with corresponding abutment surfaces the driven-side transmission case. The abutment surfaces of the transmission case are substantially coplanar with each other.