Abstract: A distance measuring apparatus is constructed to project light toward an object to be measured, receive reflected light thereof at a position according to the distance to the object to output a position signal, generate a distance computation value based on the position signal, integrate the distance computation value with an integrating capacitor, detect the distance, based on distance data corresponding to the integral result, charge the integrating capacitor by letting a constant current flow for a predetermined time, and calculate a voltage of the integrating capacitor. In the distance measuring apparatus, the distance to the object is detected, based on a correction voltage being the voltage calculated in a ranging routine, a reference voltage of the integrating capacitor preliminarily calculated before the ranging routine, and the distance data. Then the apparatus can reduce a ranging error due to change in the capacitance of the integrating capacitor.

Abstract: A far-side signal (I.sub.2) output from a PSD which has received reflected light from an object to be subjected to distance measurement is input to a clamp circuit through a second signal processing circuit, and the far-side signal (I.sub.2) or a clamp signal (Ic) at a predetermined level, i.e., a signal (I.sub.2 c) at a higher level is output from the clamp circuit. An arithmetic circuit and an integration circuit receive a near-side signal (I.sub.1) output from the PSD and the signal (I.sub.2 c) output from the clamp circuit and calculate an output ratio signal (I.sub.1 /(I.sub.1 +I.sub.2 c)). A CPU obtains a distance signal from the output ratio signal in accordance with a transformation formula which changes depending on the threshold value for determining whether to clamp the signal.