A system for protecting audiovideo content during storage and playback on systems with open buses receives a multiplexed signal, including a plurality of AV signals and decryption keys. Subsequent reads of the relocated data directed to binary cache. A value of difference which represents a degree of difference between the obtained characteristic amounts of the right-hand front wheel and the right-hand rear wheel is calculated. This structure enables simplified opto-electric circuitry to be used to read the packet header, and also enables the packet header to be used to derive the clock information required to read the high data rate information from the packet payload. According to the present invention, an increase in interval between each roller gear fixed to a corresponding one of a pair of rollers and a corresponding one of two roller driving gears meshing with the respective roller gears is suppressed compared to an increase in interval between the roller gears, fixed to the respective rollers.