A relay system includes a first relay device, a second relay device, a controller, and a route advertisement unit. The second relay device receives route advertisement from the first relay device. If an excess of a number of pieces of routing information registered in a routing table of the second relay device over a maximum number of pieces of routing information registrable in the routing table is predicted, the controller controls a number of pieces of routing information that are to undergo the route advertisement from the first relay device to the second relay device. The route advertisement unit performs the route advertisement to the second relay device after excluding, from pieces of routing information registered in a routing table of the first relay device, a piece of routing information set not to undergo the route advertisement as a result of the control of the number of pieces of routing information by the controller.