To provide a control method and a controller for a router that a prescribed QoS can be warranted.

This invention provides the router that routes packets from its own station node to its adjacent node by using a routing table including a routing probability with respect to each adjacent node. The controller 10 for the router receives the required service quality for the transmission of packets from a sender communication terminal connected to a sender node. After transmitting a forward ant agent having the received service quality from the sender node to a destination node, the destination node receiving the forward ant agent returns a backward ant agent to the sender node. When each node receiving the forward ant agent discriminates that a path formed by the forward ant agent not satisfy the service quality stored in the forward ant agent, each node aborts the forward ant agent.