A storage unit for recording on a portable recording medium identification information which is peculiar to the portable recording medium, includes a number generation part for generating a firmware management number based on a version number of a firmware of the storage unit and a number of times the firmware is installed in past in the storage unit and other storage units, an information generation part for generating the identification information based on at least a medium generation consecutive number which indicates a number of times the identification information is recorded on portable recording mediums and the firmware management number, and a recording part for recording the identification information on the portable recording medium.