PURPOSE: To measure the use rate of a processor without any hardware timer by executing repeatedly an instruction whose execution time is already known in idling operation, finding the idling time from the frequency of execution within a designated time, and calculating the use rate of the processor from the idling time.

CONSTITUTION: A display for a processor in-use state is set in a process C which is actuated at a clock period, and a process A is started by an initialization routine after the process C is ended. Then, the process A performs execution control processing, and resets the in-use display after the execution to reset an interruption mask. Then, the time up to the setting of the in-use display in the process C is defined as the idling time, and the instruction whose execution time te is already known is executed repeatedly in the idling time while an idle counter 2 counts up by one every time the instruction is executed once. Then, a process B (not shown in figure) which is started at a period T reads the value I of the counter 2 and calculates the use rate d of the processor in the designated time period T by using such an equation that processor use rate D=(T-I×te)/ T, and the idle counter 2 of the process A is cleared.