A processing unit (processor) performs processing of programs. A monitoring unit measures the rate of operation of an instruction processor in the processing unit. Information which is a standard for judging modification of the performance is stored in a control information memory unit. A control unit judges on the basis of the operation rate of the processor collected by the monitoring unit and the control information stored in the control information memory unit whether it is necessary to modify the performance or not and controls to modify the performance of the processor on the basis of the judged result.