To provide a communication system which maintains a dual power supply apparatus inexpensively and improves reliability of a system.

A monitoring means 11 monitors operations of a power supply apparatus 30 by acquiring power supply information of the power supply apparatus 30 at real time. A communication stopping means 12 stops a data output to buses 16 and 17 in the case that an anomaly of the power supply apparatus 30 is detected by the monitoring means 11. A dip switch 13 switches a state between the state to function the communication stopping means 12 and the state not to function it.