PURPOSE: To make it possible to judge a scorched color only by a single detector, by providing a light source or a light source, wherein the spectroscopic characteristic of a light receiving element has a specific one, and the light receiving element of a light detection means and measuring the quantity reduced in the quantity of reflected light.

CONSTITUTION: Almost white light emitted from a light source 1 is reflected at the surface of an object 3', of which the scorching color must be measured, to generate reflected light 4. In this case, a cut filter 5", which passes the orange color of the reflected light 4 and has a light permeable characteristic almost flat in the side of a wavelength longer than 530nm, is provided while a light quantity detection circuit 8, which includes a microcomputer for calculating the quantity of light transmitted through said filter 5" and detected upon the incidence to a light receiving element 7, is provided. Then, the quantity of light L1 prior to heating and that L2, after scorching is generated by heating, are detected and L2/L1 is calculated by the detection circuit 8 to judge a scorching degree. By this method, a plurality of filters or light detectors are not required and a scorching color can be judged by simple constitution.