The invention is objected to perform fixing in an optimum fixing condition even with various kinds of recording materials or the like while improving usability by discriminating the kinds of recording materials An image reading sensor 123 includes a reflective LED 301, a transmissive LED 303 disposed on the opposite side relative to a recording material 304 for detecting the transmitted amount of light, a CMOS area sensor 211, and an imaging lens 1113. The light from the reflective LED 301 as a light source is applied toward the surface of the recording material 304, and the reflected light from the recording material 304 is collected via the lens 303 and an image is formed on the CMOS area sensor 211. The LED 301 is disposed so as to apply LED light to the surface of the recording material 304 diagonally at a predetermined angle.