In a radar device mounted in a host vehicle, a radar transmitting unit transmits a radar signal; a light detection unit detects ON or OFF of a light of another vehicle in which the radar device is mounted; and a timing control unit sets a transmission timing of the radar signal and a light ON timing of a light of the host vehicle, the light ON timing is synchronized with the transmission timing on basis of detected ON or OFF of the light of the other vehicle. The set transmission timing is different from a transmission timing of a radar signal of the radar device mounted in the other vehicle.