With an external memory to be inserted and removed through an adapter, insertion and removal of the external memory are reliably detected and data destruction with insertion or removal is prevented. A detector includes a card detection section (32) for detecting that a memory card (10) has been inserted into a connector (31), acquiring the ID of the detected memory card (10), and acquiring card information of the memory card (10), an application section (36) for making an access request to a memory card, and a card access section (34) for acquiring the ID of a memory card (11) inserted into the connector (31) at the time of the access request, making a comparison between the ID of the memory card (10) and the ID of the memory card (11), determining whether or not the IDs are identical, and acquiring card information concerning the memory card (11) if the IDs are not identical.