PURPOSE: To detect a surface defect with high accuracy without being influenced by the ground color, by scanning a surface to be inspected, by laser lights of red, blue and green, detecting the quantity of light of each color irregularly reflected from the surface to be inspected, and deriving its mutual light quantity difference.

CONSTITUTION: Spot light of a laser projecting part 11 consisting of a red laser light projecting part 22a, a blue laser light projecting part 22b and a green laser light projecting part 22c is radiated to a surfce to be inspected S of an object to be inspected 24. Irregular reflection light from the surface to be inspected S is made to pass through a red filter 12a, a blue filter 13a and a green filter 14a through an integration sphere 2', and is photodetected by photoelectric multipliers 12W14. The time when said each photoelectric multiplier photodetects a reflected ray of a part corresponding to a flaw is shifted by a portion corresponding to an irradiation interval of each laser spot light. Accordingly, its photodetecting quantity signal is inputted to differential amplifiers 15W17, a mutual differential value is derived, this differential value is inputted to comparators 18W20 and is compared with a reference value V0, by which a defect detecting signal is obtained.