PURPOSE: To store with use of a small number of memories by dividing a data matrix into sections in accordance with a rule, storing two data, i.e. the contents of element data and 'X' when all the element data of a certain section are the same, or successively storing the element data in each section when the data are not identical.

CONSTITUTION: The data matrix 2 is divided into plural sections 4 and respective element data 1 in each section are read out and stored as stored data 5. When all the element data 1 in one section 4 are the same, two storage data 5, i.e. the contents of one element data 1 and 'X', are substituted for all the element data 1 and stored. When respective element data 1 in one section 4 are not identical, respective element data 1 are successively stored as stored data 5 in the determined order.