The present invention relates to a terminal device and a backup system, more particular to a terminal device used in a computer system. The computer system comprises a main system providing a management service to the terminal device registered in management information; a backup system standing by for continuing to provide the management service in case of occurrence of a fault in the main system; and a monitoring device monitoring an operation status of the main system. The terminal device includes a transmitting unit sending the registration request for registering in the management information to the main system and a request unit sending, if not receiving the registration completed notification to the registration request corresponding to the main system under a predetermined condition, the registration request to the backup system.