A control system 10 may include a packet size analysis unit (14) that analyzes a distribution of packet sizes of traffic input to VNFs, a capacity calculation unit (123) that calculates a traffic volume per unit time processible by one VNF based on VNF capacity information indicating a traffic volume (bps, pps) per unit time processible by one VNF for a packet size and the distribution of the packet sizes input to the VNFs, and an installation number calculation unit (124) that calculates the number of VNFs to be increased or decreased based on the traffic volume per unit time processible by one VNF and the resource amount necessary for forwarding of the traffic.