An apparatus has a plurality of printed board units each including a printed board, a frame to have the printed board arranged therein, a first rail to be arranged at a first lower end of an inner wall of the frame having the printed board located thereon in a lower opening of the frame, and a second rail to be arranged at a second lower end opposed to the first lower end in the opening; a housing including a rail holding unit to movably hold the first rail of a first printed board unit and the second rail of a second printed board unit adjacent to the first printed board unit among the plurality of printed board units; and a cooling fan to be arranged on an upper side or underside of the housing to send air into the frame.