PURPOSE: To realize a novel method for inspecting a surface which can effectively and easily detect an abnormal position of a surface to be inspected irrespective of irregularity in illumination intensity of the surface to be inspected by an illuminator.

CONSTITUTION: A method for inspecting an abnormal part of a surface to be inspected having the steps of illuminating the surface to be inspected, reading an image of the illuminated part by a reader to convert it into a signal, and processing the signal with a threshold value, comprises the steps of dividing a read area of the reader into a plurality of areas A, B, C having substantially equal light intensities based on a standard distribution of the intensity of an image 30a of the illuminated part read by the reader, and setting threshold value levels to Ea, Eb, Ec at the respective areas.