A packet relay device has a packet receiving unit, a switch, a packet sending unit, an associative memory, and a packet search unit. The packet search unit has action registers which hold information specifying an action to be executed, holds address range information including consecutive address ranges of the associative memory and the action registers in association with each other, and registers a plurality of flow entries at a plurality of addresses in the same address range. The flow entries have conditions identifying the flows associated with the same action. The device inputs header information of the packets into the associative memory, determines the action to be executed in accordance with information read out from the action register corresponding to the address range including an address output from the associative memory, and executes the determined action.