A first shielding case of a receptacle respectively has arms extending to a forward side to be forwardly folded back from proximal ends fixed to a back end of an upper surface wall, stopper walls formed on free ends of the arms and projecting from outside to inside of the first shielding case and abut on an unauthorized plug in inserting the unauthorized plug, plug pickup parts formed on the free ends of the arms and are integrally formed in parallel with the stopper walls and projecting from outside to inside of the first shielding case and abut on an authorized plug in of inserting the authorized plug, and holes formed near to an opening of the upper surface wall, the holes into which the stopper walls and the plug pickup parts are inserted, on both ends of a width direction.