Provided is a control device capable of reducing power consumption in a control system. The control device includes a master control unit and at least one slave control unit that is connected to the master control unit via a communication line. The master control unit includes a circuit for, upon completion of data transmission from the slave control unit via an uplink, transmitting an instruction for deactivating the uplink to the slave control unit via a downlink, as well as a circuit for, in order to obtain data from the slave control unit, transmitting an instruction for activating the uplink to the slave control unit via the downlink. The slave control unit includes a circuit for keeping the downlink active, and for activating/deactivating the uplink in accordance with an instruction from the master control unit transmitted via the downlink.