To prevent lowering of the resolution of an optical system used in a surface inspection apparatus.

When the surface state of a specimen 4 is detected by having the surface of the specimen 4 irradiated with a light source 10 and lenses 11-13, receiving a plurality of reflected light 25a, 25b and 25c, having a different reflection angle range using lenses 21-23 and a trihedral prism 24, and picking up a plurality of images by means of light-receiving elements 25a, 25b and 25c, resolution is prevented from lowering by setting the aperture angle of illumination light irradiated via the light source 10 and lenses 11-13 larger than that of a focusing system.