A control device includes an information analysis unit that measures communication volume in each flow included in input traffic and generates traffic information including information representing at least the measured communication volume of each of the flows and a time at which measurement is taken; a reduction target selection unit that generates ranking information representing a ranking which is a rank order of a communication volume of each of the flows in the input traffic and selects a flow having the ranking that has a trend to change in a particular direction as a reduction target flow whose communication volume is to be reduced; and a traffic control unit that reduces a communication volume on the reduction target flow, and transmits the reduction target flow subjected to the reduction processing together with another flow included in the input traffic as output traffic.