A relay device (30) receives a standard radio wave transmitted from a transmitting station (10) and containing time data, i.e. a time code. The device (30) transmits a relayed radio wave containing the time code received, at a first intensity. When the device (30) receives a transmission command code transmitted from a time-data receiving apparatus (50), it transmits the relayed radio wave for a predetermined time (10 minutes) at a second intensity that is lower than the first intensity. When a time-correction switch is operated, the time-data receiving apparatus (50) transmits a transmission command code to the relay device (30). The time-data receiving apparatus (50) receives the relayed radio wave transmitted at the second intensity from the relay device (30) in response to the command code and corrects the time on the basis of the time code it has received.