To provide a pattern matching method which is hardly affected by stain by friction, blotting, non-uniform printing or thinning, and a device to be used for executing that method.

Expanding processing is applied to dictionary data (pattern images) to become matching candidates, shrinking processing is applied to these pattern images (step 13), the differential image of these expanded and shrunk images is obtained (step 15), a mask image is generated on the basis of the difference image (step 16) and concerning pixels in the areas except for the generated mask image, matching processing is performed to an image containing a character to become a recognition object on the basis of the pattern images.