PURPOSE: To dispense with a masking register by controlling a device so that initial values are set for some N bits, and simultaneously, the inverted value of the bit in a comparison value to which one bit, at least, other than said N bits corresponds is set for said one bit.

CONSTITUTION: A decoder 4 sends a set signal to a register 9 corresponding to least significant N bits besides the register corresponding to the instructed N bits. Simultaneously with it, the decoder 4 sends a select signal so that selectors 11,12 and 13 select input data 5. Thus, a set value selecting device 6 selects the value of the input data to be selected by the selector 14, and the output of the selector 14 is inputted to the register 9 through the selector 13 in s counter 1, and the set value is set. Therefore, not only the masking register necessitated in the past comes unnecessary, but the control of mask processing comes unnecessary as well.