PURPOSE: To make it possible to inspect the state of a surface positively at a high speed without complicating the system, by periodically arranging slits having different transmittances, illuminating the surface of a body to be inspected with slit light beams having different intensities, picking the image of the surface in the specified scanning direction, and processing the output signals.

CONSTITUTION: Slits having different transmittances are alternately arranged on a multiple-line chart 1a of a lighting part 1. The surface of a body to be inspected 2 is illuminated with light from the lighting part 1. The image of the surface is picked up by a TV camera 3 so that the projected images 1b are in parallel with the horizontal scanning direction. The output signal are differentiated with a differentiating circuit 5. A differential output 5a undergoes binary coding in a binary circuit 6. A binary signal 6a from the circuit 6 and an inspection-range setting signal 7a from an inspection-range setting circuit 7 are inputted into an AND gate 8, in which an AND value is operated. An output signal 8a from the gate 8 is inputted into a pass-or- fail judging circuit 9, and the pass or fail of the state of the surface is judged. The detection of irregularities 2a which are yielded by the change in linear state of the multiple-line chart 1b projected on the surface, is ensured.