A distance measuring device comprises a motor (120), a control box (130) and a code disc (150). Relative rotation occurs between the control box (130) and the code disc (150) driven by the motor. A point position tooth (151A) is comprised on the code disc (150). The control box (130) comprises a distance measuring unit (142), a detection part (144) and a control unit (140). The detection part (144) comprises a light emitter (1440) and a light receiver (1441) which are correspondingly arranged. The control box (130) is rotated relative to the code disc (150), so that the point position tooth (151A) passes through a corresponding position between the light emitter (1440) and the light receiver (1441); the control unit (140) receives the signal output of the light receiver (1441), judges the information on alignment status of the point position tooth (151A) with the corresponding position, and sends a start or stop operation instruction to the distance measuring unit (142) on the basis of the status information. A method for seeking a distance measuring starting point is also provided, scan data is obtained by using a synchronous scanning mode of the code disc, and the starting point is judged on the basis of the output waveform of the code disc.
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