The present invention aims to provide a time authentication device for distinguishing 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 11, a time-relation information storage unit 104 stores a playback-device-time measured by a clock unit 203 of a playback device 12, and also stores a distribution-device-time measured by a clock unit 103 when the playback-device-time is acquired. The time authentication unit 107 acquires from the playback device 12 a target time measured by the clock unit 203, and also acquires an authentication time measured by the clock unit when the target time is received. The time authentication unit 107 then calculates a first difference (=Authentication Time−Distribution-Device-Time), a second difference (=Target Time−Playback-Device-Time), an authentication difference (=First Difference−Second Difference). If the authentication difference is smaller than or equal to a predetermined threshold, the time authentication unit 107 judges that the clock unit 203 of the playback device 12 is valid.