A communication system switches a communication state from a first communication state where a wireless communication unit of a communication device performs data communication and voice communication with an external device and a phone device to a second communication state to perform the data communication between the phone device and the external device, in response to electric power supply to the wireless communication unit being interrupted. The first communication state is set with a communication-device network ID used for the communication device and a phone-device network ID used for the phone device. The second communication state is set with the phone-device network ID used for the communication device and the communication-device network ID used for the phone device.