To prevent a rotating speed detecting device, which is suitable as a device for detecting the rotating speed of the wheels of a vehicle, from incorrectly detecting the rotating speed by disturbances such as vibrations.

A wheel speed sensor 14 consists of a rotor with an irregular surface which rotates eccentrically with respect to a wheel 12 and an electromagnetic pickup sensor, arranged at a location facing the irregular surface. When the wheel is rotating, the signal with undulation caused by the eccentricity of the rotor which is superimposed on the waveforms, in the form of pulses caused by the irregular surface, is outputted from the electromagnetic pickup sensor. When undulation is not superimposed on the signal, the signal is judged as being not caused by the rotation of the wheel 12 but as being caused by disturbances such as vibrations.