In switching by failure, no switching is performed when a packet of IP packet is lost or a packet has not arrived even when a predetermined time has elapsed, which are not recognized as a failure. There is provided a duplicate transmission path switching device for data packets having the same information configuration to a main transmission path and an auxiliary transmission path. The device includes a transmission failure monitoring unit for monitoring a transmission failure of the main transmission path; a switching receiving unit arranged at the downstream of the transmission failure monitoring unit capable of receiving a packet from the main transmission path during a normal mode, and switching to the auxiliary transmission path to acquire a packet from the auxiliary transmission path in a predetermined mode; and a switching command output unit used when the monitoring result shows that a transmission failure is present, for outputting a switching command capable of switching to the auxiliary transmission path before the transmission failure reaches the switching/receiving unit, to the switching/receiving unit.