A first card slot extends along a first imaginary plane. A second card slot extends along a second imaginary plane parallel to the first imaginary plane. A printed wiring board is placed between the first and second imaginary planes. A first connector is mounted on the front surface of the printed wiring board. The first connector receives a first card coming through the first card slot. A second connector is mounted on the back surface of the printed wiring board. The second connector receives a second card coming through the second card slot. A guiding member defines a first guiding surface extending along the first imaginary plane and a second guiding surface extending along the second imaginary plane. A space is efficiently utilized at the back surface of the printed wiring board. The first and second cards are enclosed in the enclosure in a layered manner.