A wafer pattern inspecting apparatus and method are disclosed. The apparatus comprises an image sensor to acquire image data from a reference die and a sample die, an external memory to store the image data, an encoder to compress the data, a decoder to decompress the data, an internal memory device to store the compressed image data of the reference die, an arithmetic module to process the image data for the reference dies to extract a reference image data, a reference storage memory to store compressed reference image data, and a comparison module to compare the sample die image data with the reference image data to an extract defect data for the sample die.