PURPOSE: To improve the compressibility of data by constituting the device so that a '0' compression processing is executed at every data in addition to a digit number compression processing.

CONSTITUTION: This device is provided with a '0' retrieving means 15 for retrieving '0' continued to the lower rank of digit number compressed data in which the number of digits is compressed, and a '0' compression processing means 16 for recompressing the digit number compressed data by a continuous number portion of '0' obtained by the '0' retrieving means 15. In such a state, first of all, by the '0' retrieving means 15, '0' continued to the lower rank of each coordinate value data is inspected. For instance, it is inspected that four '0's are continued to the lower rank in an X coordinate value 0123560000 of a start point. It is expressed as 012356×104 by the $0' compression processing means 16. When other coordinate value data is also processed in the same way, for instance, a start point (12356×104, 002259×104) and an end point (01565×105, 002259×104) are obtained as data 17 obtained after '0' compression. In this case, power numbers 4, 4, 5 and 4 of the respective data 10 become a result value of the '0' compression. This data 17 after the '0' compression is stored in a drawing master file 8 by a store processing means 13.