PURPOSE: To efficiently compress data and to efficiently utilize a storage space by computing input seal impression data and pattern seal impression data in an operation system for storing seal impression data.

CONSTITUTION: When a processing start request 1 is outputted, a seal impression reading means 2 converts a seal impression into bit image data and input seal impression data are formed in an input seal impression file 3. Pattern data 7 in a pattern master file 6 are extracted by the specification of pattern data 5 and input seal impression data 4 and pattern data 7 are computed by an arithmetic means 8 input data and pattern data. Then, the data are compressed by a data compressing means 9 and storing data 11 are formed in a storing data file 10. Consequently, the storage space can be reduced.