PURPOSE: To detect accurately the unevenness of painting, and to automate the inspection by irradiating a coating surface with light in follow-up to a painting action of a robot, and detecting the coating level with the quantity of transmitted light.

CONSTITUTION: A photosensor S is turned on the basis of a command signal from a controller simultaneously with the start of the painting action of a robot. Since a light emitting element is attached to the rear of a brush 2 of a coating device T, the light is irradiated to the coating surface of a primer P in follow-up to the movement of the brush 2 and detected by a photoreceptor. Accordingly the unevenness of the paint coated on a transparent panel can be accurately detected.