PURPOSE: To provide the recognition method capable of a recognition corresponding to the size change of an object in an image by extracting the direction component of an outline element from the outline of a detected image extracted from an image picked up with the image of the discriminating object, and preparing a normalized histogram from the distribution of relative frequency for each direction component.

CONSTITUTION: When the work image of a reference work is inputted from an image input device 2, the outline of that work is extracted by an image processing part 3. The image processing part 3 displays the external size and hole or the like of the reference work as drawings shown by the outline by performing smoothing processing, differential processing and binarizing processing. This drawing is transformed into a chain code for each positioning candidate section such as a corner part or a hole by a chain code transformation part 4, and the normalized histogram is prepared from the chain code by a normalized histogram preparation part 5. Concerning the normalized histogram, normalization is performed by taking the direction exponent of the chain code on an abscissa and the relative frequency of the direction component of the chain code expressing the drawing on an ordinate.