To improve the aging efficiency and the failure detecting efficiency.

A microcomputer comprises a command decoder 121 for generating control signals on the operation by decoding the transmitted command code and a mode decoding unit 121B for executing the operation of the predetermined command in a different manner from the original operation of the predetermined command according to the mode instruction from the outside when constituting the microcomputer including a command execution unit for performing the operation based on the output. The aging efficiency and the failure detecting efficiency can be improved by allowing a customer program to be used without any changes when selecting a chip by the aging or an LSI tester even when the customer system is dependent on the hardware.