Receiver (2) sequentially switches a preset frequency change amount in stages from a large value to a small value. According to the reception side frequency change amount, the reception side frequency candidate for detecting a synchronization signal is calculated. Synchronization signal detection unit (5) detects a synchronization signal transmitted from a transmission device by using the calculated reception side frequency candidate. Moreover, transmitter (1) calculates a transmission side frequency candidate as a frequency candidate for transmitting the synchronization signal according to the largest possible frequency change amount calculated according to the bandwidth of the synchronization signal. When the calculated transmission side frequency candidate exists in the system frequency band, the calculated transmission side frequency candidate is determined to be a synchronization signal frequency for transmission of the synchronization signal, and the synchronization signal is transmitted from synchronization signal transmission unit (4) to receiver (2).