PURPOSE: To decrease the quantity of information that is stored outside a microprocessor LSI chip and to reduce the switching time of the process level, by storing a register memory having large capacity and a comparatively low speed and a register memory of small capacity and a high speed into the LSI chip.

CONSTITUTION: A microprocessor LSI chip contains a register 1 of small capacity and a high speed and a register 2 of large capacity and a low speed with a small occupied area. An arithmetic process is carried out by an arithmetic circuit 3 and based on the contents of the register 1. In this case, both outputs of the comparators 62 and 63 are inverted to O via a level memory 4, a level register 5, etc. if the information of the process level which is now under execution. Then the contents of the register 2 is read out based on the control signal supplied from a control circuit 12 and then written into the register 1 via a switching circuit 8. Thus an arithmetic process is carried out through the circuit 3 and based on the information of the register 1. Owing to an LSI chip storing a register which has substantially large capacity, the quantity is reduced for the information to be stored in a memory outside the LSI chip. Thus the switching time is reduced for the process level.