MALFUNCTION PREVENTING METHOD

PROBLEM TO BE SOLVED: To eliminate danger for a controlled system part to be erroneously controlled by always turning on the power source of a monitoring system but turning on the power source of a driving system only when controlling the controlled system part. SOLUTION: The power supply system of a centralized controller is separated into the monitor system (supervisory system) and the driving system. Namely, a power source circuit 31 for generating a power supply voltage VM5 for the monitor system from a voltage V48 and a power supply circuit 32 for generating a power supply voltage VD5 for the driving system from the voltage V48 are provided. When a control terminal tc of these power supply circuits 31 and 32 is turned to a ground potential, a circuit becomes a driving state. In this case, the monitor system power source 31 is always turned on but the driving system power source 32 is turned on only when it is necessary to control the controlled system part. Since no power is supplied to the driving system in an operation monitor mode for the controlled system part, even when a microprocessor runs away and erroneous control data are written into a control port, these erroneous contorl data are not sent to the contorlled system part.