An ultrasonic rangefinder capable of effectively removing high-level, directly transmitted wave components. The rangefinder can be used even at low temperatures. The rangefinder comprises an input signal-processing circuit, an output signal-processing circuit, and a gain control circuit inserted between the input and output signal-processing circuits. The output signal-processing circuit includes a reception amplification circuit and a detection circuit, the reception amplification circuit having an amplifier. The gain control circuit lowers the gain of the reception amplification circuit to raise the undetected and detected input voltage levels applied to the detection circuit. The gain control circuit comprises three control devices. The first control device is driven into conduction when its input pulse signal varies from a low level to a high level. The second control device reduces the feedback resistance of the amplifier of the reception amplification circuit in response to conduction of the first control device. In response to conduction of the first control device, the third control device controls the time for which the second control device operates.