A knock pin (50) is inserted into a knock hole (54) of an electric motor case (18) to which a resolver stator (30) is fixed. The resolver stator (30) is positioned by engaging the knock pin (50) with an engagement groove (56). The resolver stator (30) includes a stop portion (58) at a position opposed to a rear end of the knock pin (50) in its insertion direction. When the knock pin (50) is about to fall off from the knock hole (54), the stop portion (58) prevents its movement, thereby preventing the falling off.