PURPOSE: To detect the direction of a substance automatically by irradiating parallel light to the substance to be detected at its direction and a sample substance, detecting and comparing their reflected light, and sending an output indicating the difference of directions when a difference is detected between both reflected light.

CONSTITUTION: Parallel light from a light source 1 is irradiated to a substance to be detected at its direction on a detecting board 2a. In this case, the light is not irradiated to optical fibers 3a located on the shadow of the substance, but is irradiated only to the optical fibers 3a located on a position other than the shadow. On the other hand, the light is not irradiated to optical fibers 3b located on the shadow of the sample substance, but is irradiated only to the optical fibers 3b located on a position other than the shadow. When the mechanical positions of the optical fibers 3a, 3b to the substance and the sample substance are made coincide with each other, an L level signal is outputted from a NOR circuit 6 only when the direction of the substance coincides with that of the sample. Thus, the direction of the substance can be automatically detected.