PURPOSE: To increase the area of a photomask obtained by one time of scanning without degrading the resolving power in detection and to improve throughput by using the signals obtained from plural signal receiving parts as detection signals and comparing the same with the scanning signals of respective reference patterns.

CONSTITUTION: Light is irradiated from a light source 1 to the pattern 4 to be inspected on a photomask, and the light transmitted therethrough is detected in the 1st signal detecting part 9 and the 2nd signal detecting part 10 via a half mirror. Stages 2, 3 are moved by an X laser interferometer 5 and a Y laser interferometer 6 to scan the entire surface of the pattern 4. The scanning signal obtd. from the part 9 is compared with the signal from the 1st pattern generating part 14 by which coincidence or dissidence is decided. Similarly, the scanning signal obtained from the part 10 is compared with the signal from the part 15, by which coincidence or dissidence is decided.