A lid has a fixing surface to be fixed to a metal board so that a metal surface, equipped with no components, of the metal board is in contact with the fixing surface, a through bore provided in laterally close proximity to the fixing surface and exposing mating parts of an external connector with which harnesses are mated, a fixing edge provided around the through bore and fixed to a housing of the external connector; and fixing pedestals projecting from a circumference of the fixing surface and fixed to the control board. A direction of connecting power supply terminals of the external connector to the metal board is a direction being perpendicular to the metal board. A direction of connecting the control board to signal terminals of the external connector is identical to the direction of connecting the power supply terminals to the metal board.