A control device is connected to at least one solar cell module and an inverter, and controls the at least one solar cell module by MPPT control. The control device includes an opening/closing unit and a control unit. The opening/closing unit includes a semiconductor relay and a mechanical relay connected in parallel with the semiconductor relay. The control unit controls opening and closing of the opening/closing unit in response to a control signal from the inverter. In a case of connecting the at least one solar cell module and the inverter, the control unit turns ON the semiconductor relay to turn ON the mechanical relay, and then disconnects the semiconductor relay. In a case of cutting off the connection between the at least one solar cell module and the inverter, the control unit connects the semiconductor relay to disconnect the mechanical relay, and then disconnects the semiconductor relay.