To provide a control device capable of reducing consumption power in a control system.

The control device comprises a master control unit and at least one slave control unit connected to the master control unit through a communication line. The master control unit comprises: means for, when data transmission from the slave control unit through an uplink is completed, transmitting an instruction for deactivating the uplink to the slave control unit through a downlink; and means for, when data should be acquired from the slave control unit, transmitting an instruction for activating the uplink to the slave control unit through the downlink. The slave control unit comprises means for maintaining the downlink to be activated and, in response to an instruction from the master control unit transmitted through the downlink, activating/deactivating the uplink.