A board includes a separating zone in an area closer to the edge than to the center of the board, the separating zone including one elongated through hole. A first group of electronic components that is a source of heat or electric noise is placed in a first area on the center side with respect to the separating zone of the board. On the other hand, a second group of electronic components from which influence of heat or electric noise from other components needs to be eliminated to a maximum extent is placed in a second area on the edge side with respect to the separating zone of the board.