An apparatus for detecting overlapped paper sheet feed in a paper sheet feed path. The apparatus includes a photosensor and a load resistor located in the paper sheet feed path for detecting a voltage representing a light transmittivity of paper sheet(s) fed through the paper sheet feed path. The apparatus also includes a resistor control for changing the resistance value of the load resistor between a first resistance which generates a predetermined detected voltage at the feed of a single paper sheet of the highest light transmittivity and a second resistance generating the predetermined detected voltage at a feed of a single paper sheet of the lowest light transmittivity and for comparing a detected voltage of a first paper sheet with the predetermined detected voltage to generate a first signal indicating that the detected voltage is equal to the predetermined detected voltage and a second signal indicating that the detected voltage is not equal to the predetermined detected voltage and for fixing the resistance value of the load resistor in response to the first signal and generating an error signal representing the overlapped paper sheet feed in response to the second signal. The apparatus also includes means for comparing a detected voltage of a second paper sheet with a first threshold voltage which is established separately from the predetermined detected voltage to discriminate a single paper sheet feed and an overlapped paper sheet feed in order to generate an error signal when the detected voltage of the second paper sheet is a voltage indicating an overlapped paper sheet feed.