a pattern defect inspection apparatus according to this invention comprises an irradiation circuit for irradiating a substrate on which a given pattern is drawn , a detector circuit for detecting said irradiated pattern on said substrate , a bit pattern generating circuit for quantizing and generating previously given design data by processing said design data based on specified figure information to obtain bit pattern data composed of a finite number of pixels , and a comparator circuit for detecting defects on said substrate by comparing the detected data from said detecting means with the data from said bit pattern generating means , wherein the bit pattern generating circuit has an additional parameter conditioner for setting the dimension of each pixel to be quantized into said bit pattern data to the desired value .