Abstract: A speed measuring device provided by the present invention comprises a base, a speed measuring circuit, and two speed measuring units. The two speed measuring units are installed on the base and located a distance away from each other. The microprocessor outputs a signal to the pulse generator, the pulse generator produces pulses and send them to the first and second frequency oscillators, letting the first and second frequency oscillators send two frequency signals to the respective infrared emitters, and then the respective infrared emitters emit infrared signals with different frequency. When the moving object passes through different areas irradiated by the different frequency infrared signals, the different frequency infrared signals will be reflected to the infrared receivers. Finally, the infrared receivers send two detecting signals to the microprocessor, allowing the microprocessor to figure out the motion data of the moving object.