In the first power mode: each packet processor of the second group maintains own operating mode in a first operating mode of relatively low power consumption; and the distributor selects the handling packet processor from the first group for the first priority, and selects the handling packet processor from at least one group excluding the second group for the second priority.In the second power mode: each packet processor of the second group maintains the own operating mode in a second operating mode of relatively high power consumption; and the distributor selects the handling packet processor from the first group for the first priority, and selects the handling packet processor from at least one group including the second group for the second priority.