PURPOSE: To detect automatically both parallel shift amount and rotary shift amount at a high speed by having comparison between centroid coordinates of a standard pattern which are obtained in the same way.

CONSTITUTION: The binary coded output pattern of a seal image to be collated which is supplied from a picture input device is supplied to a pattern memory 1-1 and stored there. The line width of said image pattern is thickened by a thickening processing circuit 2, and the result of this thickening processing is stored in a pattern memory 1-2. Then a centroid detecting circuit 3 obtains centroids G1WG9 for the patterns of remaining blank regions A1WA9 respectively. The coordinates of obtained centroids G1WG9 are supplied to a shift amount calculating circuit 4. The circuit 4 compares the centroid coordinates of plural remaining blank regions of the seal image pattern supplied from the circuit 3 with the centroid coordinates of the remaining blank regions underwent the thickening processing which are obtained in the same way for the standard seal pattern registered to a standard pattern file 5. Thus the pattern shift amount is calculated.