PURPOSE: To execute picture overlapping with high accuracy by correcting (eliminating or restoring) the deficiency part of an input picture and by forming the parameter for pattern matching.

CONSTITUTION: Picture data and the density pattern of the designated registration picture are read from a file 60. The designated picture data are stored in a picture memory device 30 and the density pattern is stored in a main memory device 20 respectively. The collation picture on an input original is read from a picture input device 50, and it is stored on the picture memory device 30. Coordinates of the rotational center of the collation picture are calculated, and then, the density pattern of the collation picture is calculated. The parameter is calculated concerning the collation picture, the required area is obtained based on the parameter, and the rotational angle of the collation picture which is necessary for overlapping of the registration picture and the collation picture is obtained. Finally, the collation picture is shifted in parallel so that rotational centers of the registration picture and the collation picture will coincide, and both pictures are overlapped by rotating by only the required angle.