PURPOSE: To prevent erroneous reading, by providing a uniform thick transparent plate having a comparatively large refractive index in contact with a light shielding plate apart from a uniform distance at each front surface of an LED and a photodetector, and sharpening the directivity between the LED and the photodetector.

CONSTITUTION: A middle part toward X axis direction between an LED1 and a photodetector 2 and a punched paper 3 having hole interval as the same interval as the arrangement interval of the LED1 to Y axis direction is moved to Z axis direction. The LED1 and the photodetector 2 are imbedded in a light shielding body 6, and only the front surface emitting and receiving light leads to a hollow part through which the paper 3 passes via a hollow cylinder. A light from the LED1 is made incident to a photodetector 2-3 after several times reflections, transparent plates 4 and 5 with uniform thickness having a comparatively large refractive index are provided on the surface of the light shielding body 6, and the directivity between the LED1 and the detector 2-3 is made sharpened, allowing to completely intercept the transmission/reception of light.