The communication apparatus including: a communication unit communicating with external apparatuses via a communication line; a notification unit notifying, from the communication unit, the external apparatuses of stop of electric power supply to a controller controlling operation, when electric power supply to the controller is stopped; an identification information memory for storing identification information of one of the external apparatuses when, after the notification unit makes the notification, the notification unit again makes the notification to the one of the external apparatuses upon receipt of a signal from the one of the external apparatuses; and a signal processor processing a signal received from any of the external apparatuses by the communication unit. The signal processor discards a signal, when a transmission source of the signal is one of the external apparatuses having the identification information matching the identification information stored in the identification information memory.