An ultrasonic ground speedometer utilizing Doppler effect comprises an ultrasonic transmitter (2) for outputting an ultrasonic wave at a predetermined angle (ϑ) against a road surface, an ultrasonic receiver (6) for receiving a reflected ultrasonic wave caused by reflection of the output ultrasonic wave from a road surface, an arithmetic circuit (12) for deriving ground speed from Doppler shift between the output ultrasonic wave and the reflected ultrasonic wave. The ultrasonic ground speedometer also includes an output frequency control circuit (13) for controlling the output ultrasonic wave frequency in such a manner as to keep the reflected ultrasonic wave frequency to a con­stant value in response to changes in ground speed. An amplification degree control circuit (14) also included for controlling the ampli­tude of the output ultrasonic wave to keep a substantially constant output intensity of the output ultrasonic wave over an output ultra­sonic wave frequency range controlled bythe output frequency control circuit.