A resin body (2) cooperates with a cover (3) made of sheet metal to form a slot (5) into which a memory card (100) is to be inserted. The resin body has an erroneous card insertion preventing thickened portion (22) into which a core member (24) made of a material that is higher in strength than the resin forming the body is embedded. The thickened portion (22) is positioned in an erroneous insertion preventing notch region of the memory card (100) that is to be inserted in a card attachment position of the slot (5) in a normal insertion posture, and is to butt against an insertion end face of the memory card (100) that is erroneously inserted in a posture different from the normal insertion posture, to block the insertion of the memory card (100) to a card set position. An end face (25) of the core member (24) is protruded from an end face (23) of the thickened portion (22).