Abstract: A Doppler radar for forecasting collision, in which three consecutive Doppler signals are obtained by radiating microwave forwardly from the front of a car, the frequency of the microwave being consecutively switched in three steps at a constant interval, and combining the aforesaid microwave and reflected microwave reflected from an object for obtaining intelligence about the distance of the object from the car front, residual time left for the object to reach the car front as well as forecasting collision or non-collision from two of the three Doppler signals and obtaining intelligence about the sense of relative velocity of the object relative to the car front from the remaining Doppler signal and one of the aforesaid two Doppler signals.