PURPOSE: To discriminate assuredly the direction of a paper sheet by performing the color separation of the received reflected light to detect a pattern having a specific size and a specific color and existing on the surface of the paper sheet.

CONSTITUTION: The paper sheets of a mail P, etc. whichis under conveyance undergo the optical scan via a light source 2. The beams excepting for a red beam of the reflected light are reflected by a dichroic mirror 3. While the red beam is transmitted through the mirror 3 and received by a photoelectric transducers 6 and 7 of a line sensor. The detection signal passes through a differential amplifier 10 and a comparator 13 to which a prescribed slice level is set detects the specific size of a fixed position and a red frame 1 of a specific pattern of the mail P with the outputs of transducers 6 and 7. This detection signal is supplied to a deciding circuit 17 via an AND gate 16 which is opened by the mask signal corresponding to a fixed external form of the post P and produced by the transducer 6 via a comparator 11 and a mask signal generating circuit 15. Then the circuit 17 can decide assuredly the direction of the mail P according to a fact whether the detected red frame signal is produced at the front end or the rear end of the mail P.