PURPOSE: To make it possible to collate also a pattern having a ground pattern on its background by collating the ground pattern with the pattern and removing the ground pattern from the collating pattern.

CONSTITUTION: A document 1 is read out by a reader 10 and the read data are sent to a ground pattern positioning/removing means 11. A data control device 12 separates only a partial area 4 including a print of a seal 3 and stores the area 4 in a picture memory 13. The control part 12 positions a background part 5 on the ground pattern previously stored in a registered ground pattern memory 14. If the ground pattern 6 can be collated in the background part 5, the whole ground pattern of the partial area 4 including the print of the seal 3 can be found out by forecasting it from the positional relation of the repeated pattern of the ground pattern 6. Thus, the pattern of the seal print from which the ground pattern is removed can be obtained by subtracting the ground pattern from the partial area 4 stored in the picture memory 13.