PURPOSE: To accurately detect a position of an elevator, even when a pulse generates its waveform abnormal by a quantity of light changed due to a certain cause, by providing a maximum voltage detecting circuit of an input signal and a voltage divider, dividing an output of the detecting circuit, with an output of the voltage divider serving as the reference voltage.

CONSTITUTION: A pulse generator 3, generating a pulse synchronized with movement of an elevator cage, is provided. This pulse generator 3 generates the pulse transmitted to an optical fiber 4 feeding a signal input. This input signal is compared with fixed reference voltage in a comparator 17 generating a square-wave pulse detecting a position of an elevator. Here providing a circuit 30 detecting a peak voltage signal of the light receiving pulse signal, a circuit (voltage divider) 36, adding in proportion to a signal of the peak detecting circuit 30 voltage, adding a predetermined gain, to the reference voltage serving as reference voltage of the comparator 17, is provided.