In an optical distance measuring apparatus, a transmitter has a light-emitting device emitting an optical signal synchronized with a modulating signal having a predetermined repetition frequency, and a modulating signal generator outputting the modulating signal to the light-emitting device. A receiver has a photodetector receiving an optical beam reflected by an object to be measured and converting it to an electrical signal, a switch receiving the signal from the modulating signal generator and alternately choosing two channels for the electrical signal with a predetermined timing, and first and second storage sections storing electrical signals on the two channels. A signal processing section has a differential operation section performing a differential operation on electrical signals stored in the first and second storage sections, and a distance determining section determining a distance to the object on the basis of the result of the differential operation of the differential operation section.