Abstract: A control system and control device are provided capable of flexibly realizing communication processing without requiring an additional unit even when a plurality of units having a communication function are present is provided. The control system includes a first unit having a first communication port for transmitting and receiving data, and one or more second units electrically connected to the first unit. Each of the second units includes a logical communication unit for transmitting/receiving data to/from the device electrically connected to the first communication port of the first unit. The first unit includes a forwarding processing unit which forwards transmission data transmitted from the second unit to the device which is a transmission destination.