To safely execute inter-arbitrary computer data transfer in a communication environment constantly constituted of the unspecific large number of computers.

In a router RT13 positioned at the upstream of a most downstream side router RT14 on a route R15 from a transmission origin computer CPU12 to a transmission destination computer CPU15, and positioned at the upstream of a most downstream site router RT11 on the router R13 from a transmission origin computer CPU13 to the transmission destination computer CPU14, packets on the route R13 are divided into a plurality of packets PT51, and packet data from the transmission origin computer CPU12 to the transmission destination computer CPU15 are embedded in a packet PT51, and made to flow through a communication network with an original packet PT52. In a router RT12 positioned at the downstream of the upstream side router RT13 on the route R15, and positioned at the downstream side of the upstream side router RT13 on the router R13, the data embedded in the packet PT51 are extracted, and the packet PT51 is abandoned.