A control device of a power supply system includes a first processing unit and a second processing unit. The first processing unit is a processing unit configured to perform a first process of determining certain strings out of a plurality of strings connected in parallel to a power distribution device. The second processing unit is a processing unit configured to perform a second process of performing inputting of electric power to the plurality of strings connected in parallel to the power distribution device or outputting of electric power from the plurality of strings to the power distribution device using at least the certain strings determined by the first processing unit.