A card unit on which a card attached to a connector and detached from it is loaded has a frame, which is loaded with the card and is expanded and contracted, and an attaching/detaching mechanism which attaches the card to the connector and detaches the card from the connector by expanding and contracting the frame. The attaching/detaching mechanism has a rotatable attaching/detaching lever which makes the frame expand and contract by its rotational operation. A maintaining part (maintaining surface parts) is provided, and the frame is maintained at a position, at which the card is disengaged from the connector, by the maintaining part.