PURPOSE: To prevent the generation of accidents or failures due to the heat generation or the like of a load by detecting the generation of abnormality such as runaway in a control means included in a slave control unit by a master control unit and inhibiting current supply to the load connected to the slave control unit.

CONSTITUTION: A CPU 110 in the master control unit 100 monitors the operation of CPUs 210, 310 of the slave control units 200, 300 to discriminate the existence of abnormality. At the time of detecting abnormality, the CPU 110 in the master control unit 100 directly controls the gate means of the units 200, 300 to interrupt correct supply to the load. Even when runaway is generated in the CPUs 210, 310 of the units 200, 300, the generation of an accident or a failure due to the abnormal heat generation or the like of the load can be prevented.