Unauthorized installation of software is prevented even at a production site at which software cannot be installed through a communication line. The memory card stores: additional software including a software ID; a recording medium ID; and encrypted information generated by encrypting the software ID, using the recording medium ID as a key. The controller performs the steps of: obtaining the encrypted information from the memory card; obtaining the recording medium ID from the memory card; obtaining the software ID by decrypting the encrypted information, using the recording medium ID as a key; obtaining the software ID from the additional software, comparing the decrypted software ID and the software ID obtained from the additional software; and storing the additional software in the storage when the comparison is successful.

Unauthorized installation of software is prevented even at a production site at which software cannot be installed through a communication line. The memory card stores: additional software including a software ID; a recording medium ID; and encrypted information generated by encrypting the software ID, using the recording medium ID as a key. The controller performs the steps of: obtaining the encrypted information from the memory card; obtaining the recording medium ID from the memory card; obtaining the software ID by decrypting the encrypted information, using the recording medium ID as a key; obtaining the software ID from the additional software, comparing the decrypted software ID and the software ID obtained from the additional software; and storing the additional software in the storage when the comparison is successful.