A monitor control system comprises an interrupt processor for executing regular monitor processing by a periodic interrupt occurring at a predetermined time interval, and a background processor for executing background processing, wherein when interruption occurs, execution of the background processing by the background processor is interrupted while regular monitor processing is executed during a period in which background processing is interrupted. The time-consuming background processing is treated as a low-level processing task, and the regular monitor processing, as a high-level processing task. The low-level processing task is executed as a background processing during CPU idle time. Interruption of the background processing occurs ever 10-msec, during which the high-level processing task is executed. Accordingly, background processing and regular monitor processing are smoothly executed, and the CPU is thereby efficiently used.