PURPOSE: To identify the surface and back instantaneously without damaging a tape or the like by irradiating a specified light on two surfaces of a tape or the like to compare the reflectance of reflected light from one surface with that of reflected light from the other surface.

CONSTITUTION: Infrared rays from infrared ray sources 12 and 14 are irradiated on one surface 10a and the other surface 10b of a tape 10 through waveguides 16 and 18 respectively while light choppers 20 and 22 are energized to interrupt the infrared rays at a specified frequency. These rays are reflected on the surfaces 10a and 10b of the tape 10 according to respective optical characteristics at a different reflectance and introduced into detectors 24 and 26 through waveguides 28 and 30 and filters 32 and 34. As a result, the detectors 24 and 26 generate detection signals corresponding to the characteristics of the respective surfaces 10a and 10b while increasing or decreasing at a specified frequency. These signals are compared with a comparator circuit 36 and the results of the comparison indicates which is the magnetic film surface or the base surface on a display 38.