A plurality of slaves include a first slave constituting the start and end points of a ring wiring and a plurality of second slaves connected between the start and end points, the ring wiring being capable of configuring a first path via which the second slaves cause data accepted from the start point side to be cyclically transferred to the end point side, and a second path for each slave to loop back the data from the device itself when the path between the slave and an adjacent slave is disconnected. When the path is recovered from the disconnection, a master transmits a command for switching the second path to the first path to the slave that carries out the loopback, and sends out data after the elapse of a time based on a propagation delay time from the time of this transmission.

Communication device is a communication device to which a plurality of slaves are daisy-chained and which communicates with the plurality of slaves. Communication device includes processor. Processor executes setting processing. In the setting processing, an update cycle of a specific slave that is a slave having a shortest data update cycle among the plurality of slaves is set to a reference cycle, and an update cycle of another slave different from specific slave among the plurality of slaves is set to an integral multiple of the reference cycle.