To provide a speed detecting device capable of accelerating the speed detecting timing of a moving body in the movement start initial stage by providing a movement stop judging means, a pulse level change detecting means, and an initial speed calculating means.

A speed detecting means (a) outputs pulses having the frequency proportional to the speed of a moving body, and a speed calculating means (b) calculates the speed of the moving body from the time of one cycle of the pulses outputted from the speed detecting means (a). A movement stop judging means (c) judges the movement stop of the moving body from the speed calculated by the speed calculating means (b). A level change detecting means (d) detects the first level change and the second level change of the pulses after the movement stop of the moving body is judged by the movement stop judging means (c). An initial speed calculating means (e) calculates the initial speed of the moving body in a half cycle from the first level change to the second level change detected by the level change detecting means (d). The delay of the speed detecting timing can be eliminated.