When a capsule is manufactured, a unique number such as a serial number is stored in non-volatile memory in the capsule. If the capsule is used with an external apparatus, the unique number is sent from the capsule to the external apparatus. The external apparatus relates each unique number with a capsule ID comprising a small number of bits in a management table formed in non-volatile memory and sends the capsule ID to the capsule, and the capsule ID with the small number of bits is set as an identifier in the capsule. In this manner, it is made unnecessary to provide a switch in the capsule for setting the identifier and it becomes possible to reduce and send the quantity of information sent as the identifier.