A controller connected to a node configured for processing a packet received in accordance with a processing rule that stipulates a matching rule and processing for a packet matching to the matching rule includes a removal request history management unit, a processing rule search unit and a processing rule setting unit. The removal request history management unit retains record(s) of requests made to the node(s) in connection with removing the processing rule. The processing rule search unit references, in setting a new processing rule for the node, the removal request history management unit to search for a processing rule having a matching rule that competes with the new processing rule. The processing rule setting unit re-requests, in case a processing rule having a matching rule competing with the new processing rule exists in the removal request history management unit, the node(s) to remove the processing rule having the matching rule competing with the new processing rule.