A packet forwarding apparatus, a communication system, and a process rule update method that can accurately delete process rules used for packet forwarding and the like include a process rule storage unit that stores process rules defining a process content for each flow; a packet process unit that executes processing a received a packet by using a process rule matching the received packet among the process rules and; an end determination information extraction unit that extracts information for checking a flow end from the received packet; and a flow end check unit that deletes, when a flow end is checked based on the extracted information, a process rule corresponding to the flow.