In a router supporting a packet relay function based on a routing table, and also a VPN (Virtual Private Network) function, an output port deciding portion decides an output port different from a normal output port indicated as an output port corresponding to a destination address of a communication confirming packet based on the routing table, and packet transmitter transmits the communication confirming packet through the decided output port. A communication confirming packet determining portion determines a communicating state based on a response packet for the communication confirming packet received from the destination router of the communication confirming packet returned from another router connected to the output port and relayed by its own router.