A packet relay apparatus includes a first packet processing circuit and a second packet processing circuit. The first packet processing circuit executes, discarding data packets from among data packets, and transferring the rest of the data packets to the second packet processing circuit, counting discard number of the data packets, determining whether or not the discard number is equal to or greater than a threshold and transferring, if the discard number is equal to or greater than the threshold, a discard number information packet including discard number information indicating the discard number to the second packet processing circuit. The second packet processing circuit executes discarding data packets from among the data packets, counting discard number of the data packets and collecting the discard number counted by the second packet processing circuit and the discard number indicated by the discard number information included in the discard number information packet.