A pattern defects inspection system inspects the presence/absence of pattern defects in a photomask as an object to be inspected in which a chromium pattern and a phase shift pattern are formed together. Measurement data output from a sensor circuit for generating measurement pattern data by inspecting measurement patterns corresponding to two types of patterns formed on the object by radiating light on the object, and two identifiable design data stored in a magnetic disk unit in advance, i.e., chromium pattern design data used to form a chromium pattern and phase shift pattern design data used to form a phase shift pattern, are read out by a bit pattern generator for performing development processing. The two types of bit data obtained by the bit pattern generator are synthesized according to the same coordinate definition. The synthesized design data is compared with the measurement data by a comparator. As a result, the presence/absence of pattern defects in the object can be determined.