The present invention has an object of realizing a defect inspection estimated at high accuracy by preparing a reference image that reflects the change of the blur with time from a sampled image and design data. The present invention comprises a point spread function estimating section 23 for estimating a point spread function from an observation image and design information, a convolution image generating section 31 for generating a convolution image by convoluting the point spread function relative to the design information and a reference image generating section 33 for generating a reference image from the convolution image obtained by the convolution image generating section. binary image relative to “chromium on quartz glass”.