A redundant system comprising: - multiple devices communicably coupled via wired communication paths, wherein - each of the devices is communicably coupled via two or more independent communication paths of the wired communication paths to two or more of the devices other than the each of the devices, - each of the devices is configured to perform wired communication via the two or more of the wired communication paths with the devices communicably coupled to each of the devices via the two or more of the communication paths in a normal state, - each of the devices as a first device comprises a wireless communication unit, and is configured to, under a condition of malfunction in two or more parts in the redundant system: perform a wired communication via the wired communication paths with each first counterpart device with which the wired communication via the wired communication path is enabled, switch from the wired communication via the wired communication paths to wireless communication and to continue communication with each second counterpart device with which the wired communication via the wired communication paths is disabled, and characterized in that: - if a signal is transmitted from the second counterpart device to the first device using wireless communication, the signal is transmitted from second group devices in wired communication with the second counterpart device and then received by first group devices in wired communication with the first device, and upon receipt of the signal, the first group devices transmit the received signal to the first device using wired communication. - multiple devices communicably coupled via wired communication paths, wherein - each of the devices is communicably coupled via two or more independent communication paths of the wired communication paths to two or more of the devices other than the each of the devices, - each of the devices is configured to perform wired communication via the two or more of the wired communication paths with the devices communicably coupled to each of the devices via the two or more of the communication paths in a normal state, - each of the devices as a first device comprises a wireless communication unit, and is configured to, under a condition of malfunction in two or more parts in the redundant system: perform a wired communication via the wired communication paths with each first counterpart device with which the wired communication via the wired communication path is enabled, switch from the wired communication via the wired communication paths to wireless communication and to continue communication with each second counterpart device with which the wired communication via the wired communication paths is disabled, and characterized in that: perform a wired communication via the wired communication paths with each first counterpart device with which the wired communication via the wired communication path is enabled, switch from the wired communication via the wired communication paths to wireless communication and to continue communication with each second counterpart device with which the wired communication via the wired communication paths is disabled, and characterized in that: - if a signal is transmitted from the second counterpart device to the first device using wireless communication, the signal is transmitted from second group devices in wired communication with the second counterpart device and then received by first group devices in wired communication with the first device, and upon receipt of the signal, the first group devices transmit the received signal to the first device using wired communication.