An OpenFlow network includes multiple controllers. Each controller includes a load control table and a load control unit. The load control table controls at least one of the number of messages which each of switches in the OpenFlow network has transmitted to a controller controlling the switch over a predetermined time and the number of packets that the switch has received over a predetermined time. When a predetermined event occurs, the load control unit detects a controller having a processing load higher than or equal to a first threshold on the basis of the load control table and places at least one of the switches controlled by the detected controller under the control of another controller.