PURPOSE: To detect chipping from width variation of reflected light by projecting parallel light at right angles to the ridge line formed of two adjacent surfaces of a body to be measured, displacing the parallel light relatively in a lengthwise direction of the ridge line, and measuring the quantity of its reflected light at some stop position.

CONSTITUTION: The ridge line of the body 4 to be measured is magnified by an ocular 14 and irradiated with the parallel light; and the positions of an X table 5 and a turntable 7 are adjusted so that the ridge line of the body 4 is parallel to the movement line of an Y table 8. Then, a motor 10 is driven to project the parallel light in a lengthwise direction of the ridge line and its reflected light is photodetected to display its photodetection state on a coordinate display device 17, thus knowing where and how wide, long, and deep the chipping is.