Abstract: The present invention comprises: a sliding member that can move slidably in directions in which a card mounted in or dismounted from a housing is inserted and ejected; a return spring for energizing the sliding member in a card ejection direction; a locking member for holding the sliding member in a position in which the card is mounted, against an energizing force of the return spring; and fixed contacts, wherein the locking member is formed from an elastically deformable plate spring, and the plate spring is formed with an anchor for anchoring the sliding member, and moving contacts that can contact or separate from the fixed contacts, wherein the moving contacts are actuated in accordance with engagement and disengagement between the sliding member and the locking member, and wherein it is detected that the card has been held in a mounting position when the sliding member has been anchored to the anchor of the locking member.