PURPOSE: To decrease the number of times of a memory access required for a calculation of a complicated sum-of-products operation by constituting a storage device of a program storage part, a decoding information storage part, a data storage part and a mode storage part.

CONSTITUTION: In a direct address mode, information related to the sum of products is written in a decoding information storage part 6. Thereafter, when the mode is changed to an indirect address mode, an address of the sum of products is not such a complicated one as a conventional example, but converted to an indirect linear address. Accordingly, as for a calculation of the sum of products viewed from an operation executing part 4, data of an address A is read in, data of an address (a) + 1 is read in, and their product is calculated. It is added to S and the foregoing is repeated until the term is ended. In such a way, the number of times of an access of a memory can be decreased to half.