An ATM switching system at each node of a network performs route changing or rerouting promptly when a failure occurs. In each of ATM switching systems at nodes N1 to N6: a route table 21 of a line interface 102 is set with conversion header information of a normal route, and an alternate routing table 25 is set with header information of one or more alternate routes. Subsequently, each line interface tests, when a packet arrives, whether or not a failure has occurred in an output line involved in the normal route, by referring to a bitmap 264 storing failure lines and a VP failures. The line interface executes header conversion by applying the normal header information stored in the routing table 21 in the case of no failure set for the normal route and by applying the header information stored in the alternate routing table 25 in case a failure has occurred on the normal route, and then outputs the packet to an ATM switch 101. Since the alternate route is promptly selected at the time of a failure of a net line and not in response to decoding a header of a received packet, the number of packets discarded due to the failure is reduced, and the rerouting operation is promptly executed even in the case of multiple failures.