Optical paper sheet checking apparatus having an automatic adjustment function

In quantitatively detecting light permeated through or reflected from a paper sheet in order to detect optical characteristics of the paper sheet, an optical paper sheet checking apparatus detects with stability and optimum precision. The optical paper sheet checking apparatus comprises a plurality of optical sensors which output signals obtained by optically detecting a pattern of a paper sheet, the optical sensors comprising light emitting elements and light-receiving elements; a driving unit which supplies a current to the light emitting elements in the plurality of optical sensors in accordance with a control signal; and a controlling unit which, while the paper sheet is not in a predetermined position, (a) supplies a maximum current having a predetermined value to the light emitting elements and thereafter supplies the control signal to the driving unit so as to decrease the supply of current, (b) determines and stores optimum values for each of the plurality of optical sensors, the optimum value being the value of current supplied when the output voltage of the light-receiving elements has changed by a predetermined value in proportion to its value at the maximum current, (c) when the paper sheet is at the predetermined position, supplies the control signal to the driving unit based on each of the optimum values which have been stored, and (d) selectively extracts the detected signals from the optical sensors and outputs detected data representing the pattern of the paper sheet.