Each of a plug and a receptacle is provided with an optical contact and a shutter mechanism. The shutter mechanisms are linkaged with each other when connecting the plug and the receptacle to each other. At least one of the plug and the receptacle includes a movable member moved with being pushed by the other of the plug and the receptacle, an urging member constantly urging the movable member toward the other of the plug and the receptacle, and a cam mechanism causes the shutter mechanism to follow movement of the movable member. The shutter mechanism includes a shutter plate having an opening and movable between a first position where the opening does not face the optical contact and a second position where the opening faces the optical contact, and a projection adapted to be fitted into the opening when the shutter plate is in the first position.