Walls are erected at both ends of an arrangement of first contacts and at locations that partition the first contacts for each signal to be transmitted, project at both ends of an arrangement of second contacts and at locations that partition the second contacts for each pair of differential signals to be transmitted, and therewith are connected to ground electrodes of a circuit board. A first shell, a second shell, and the like are mounted to a first housing and a second housing in such a manner as to be spaced apart from and cover the first contacts, the second contacts, and the walls and are connected to ground electrodes of the circuit board.