A network system includes: a plurality of base stations, each with which a mobile station communicates; a core network to include one or more gateways, each with which the plurality of base stations communicates; a plurality of offload devices, each arranged between the base station and the gateway, each to serve as the gateway of an anchor point at which traffic to be offloaded is transmitted to or received from an offload network, and each to serve as the gateway of a relay point at which the traffic to be offloaded is relayed between the anchor point and one of the plurality of base stations with which the mobile station is communicating; a control station to control the traffic between the mobile station and the gateway; and one or more interception devices, each to intercept the traffic between the control station and the gateway.