An apparatus receives load information indicating a magnitude of a processing load, at a predetermined interval, from each transfer device in a network, and receives, from each communication device that performs communication through one or more transfer devices, a reporting packet for reporting information on a flow transmitted by the each communication device. The apparatus specifies, using the reporting packet, a first flow transferred through a first transfer device having a processing load greater than a detection threshold for detecting a congestion warning, as a candidate for a flow whose path is to be changed when congestion occurs, and transmits a first packet for shortening a transmission interval of a first reporting packet including information on the first flow, and a second packet for lengthening a transmission interval of a second reporting packet for reporting information on a flow transferred in the network without passing through the first transfer device.