A time authentication device identifies clocks that show a time falling within the predetermined permissible range as compared with a time shown by the time authentication device. In a time authentication device embodied as a distribution device, a time-relation information storage unit stores a playback-device-time measured by a clock unit of a playback device, and also stores a distribution-device-time measured by a clock unit when the playback-device-time is acquired. The time authentication unit acquires from the playback device a target time measured by the clock unit, and also acquires an authentication time measured by the clock unit when the target time is received. The time authentication unit then calculates a first difference, a second difference, an authentication difference. If the authentication difference is smaller than or equal to a predetermined threshold, the time authentication unit judges that the clock unit of the playback device is valid.