PURPOSE: To realize highly precise measurement by analogizing the current signals outputted from the output terminal of a light receiving element as time- integrated charging quantity and digitalizing it for positional calculation thereafter.

CONSTITUTION: The voltages V01 and V02 outputted from noise eliminating circuits 411 and 421 connecting with the output electrodes 201 and 202 of a light receiving element 200 have no temperature dependency and show a quantity proportional. to the current comprised of reflection spot light element. In addition, integration circuits 310 and 320 are constructed in the same manner, so their proportional constants are the same. The voltages V01 and V02 are respectively inputted into AD conversion circuits 610 and 611 to be changed into digital signals V01 and V02 and they are held by the holding elements 621 and 621 of a holding circuit 620 according to the holding selection signal issued from a timing generation circuit 700, then they are inputted into the address terminal of an ROM element 630. Calculation result data stored in advance are outputted from the output terminal of the element 630 and the spot lightreceiving position of a semiconductor position detecting element 200 is calculated for calculating distance measurement.