PURPOSE: To eliminate necessity for securing any excess bank setting register or the like and further to perform access to a register in a short time.

CONSTITUTION: Concerning the system for access to the register in a microcomputer equipped with plural control registers to control function blocks 12, 13, 14 and 15 and the normal registers, first of all, when the access is performed to the control registers, the access to the other registers in the function blocks 12, 13, 14 and 15, where the control registers are existent, is turned to an enable state.