A distance measuring device may be constructed utilizing a reduced number of components by calculating distance on the basis of the duration of an integration. Pulsed light is projected toward an object. A selecting circuit selectively outputs one of a pair of output voltages from two current-voltage converting circuits, each of which is connected to a position sensitive device which is configured to receive light reflected from the object. A variable-gain amplifying circuit is used for amplifying the selected output voltage and for producing an amplified output voltage. The output voltage of the amplifying circuit is integrated by an integrating circuit. Reference voltage generating circuitry generates two reference voltages having different levels and a comparing circuit compares the output voltage of the integrating circuit with one of a pair of reference voltages. Gain selecting circuitry is used for determining the gain of the variable-gain amplifying circuit on the basis of the output result of the comparing circuit. The distance to the object is determined in accordance with the duration of time that integration is performed by the integrating circuit until the integrated output voltage exceeds one of the reference voltages. Thus, distance may be determined in accordance with the magnitude of the integrated output voltage, the number of times integration is performed or the number of light projections performed by the device.