This invention relates to a conversion table compression method of compressing a conversion table and storing the conversion table in a storage medium, including an axial difference creating step of creating an axial difference table by calculating, from data stored in the conversion table, the difference values between grid points adjacent in predetermined directions along a plurality of axes which define the input space of the conversion table, a compressing step of compressing the axial difference table to create compressed data, and a storing step of storing the compressed data in a recording medium.