A gateway apparatus including: a route control packet generating unit that generates a route control packet for constructing routes between node apparatuses forming an ad hoc network and the gateway apparatus; a channel designation signal generating unit that generates channel designation signal for designating a second channel different from a first channel on which the ad hoc network transmits and receives packets; a time designation signal generating unit that generates time designation signal for designating switching time to the node apparatus for switching the channel used for transmission and reception of packets to the second channel; a radio communication unit that transmits the route control packet, the channel designation signal and the time designation signal on the first channel; and a channel switching unit that switches, when it is time to switch, the channel on which the radio communication unit transmits and receives a signal to the second channel.