The present disclosure discloses a step counting device that includes a motion detection circuit, a storage circuit and a processing circuit. The motion detection circuit detects a body movement to generate a detection signal. The processing circuit executes computer executable commands to execute the steps outlined below. The detection signal is received from the motion detection circuit. Key data points from the detection signal and representing a simplified waveform are approximated and stored in the storage circuit, each corresponding to a turning data point within a predetermined time period of the detection signal. Periodic waveform sections in the simplified waveform are identified, wherein an error value of waveform parameters between each two of the periodic waveform sections is smaller than a predetermined value. A step group count including a left step and a right step corresponding to each of the periodic waveform sections is accumulated.