In a packet network having a plurality of local switching units (1-1 to 1-k) each connected to a plurality of packet lines (9-1 to 9-ℓ; 9'-1 to 9'-ℓ) and at least one cross-connect unit (2) connected to each local switching unit through at least one transit line (10) having a predetermined transmission capacity, a plurality of virtual paths (VP) for interconnecting the plurality of local switching units through the cross-connect unit are defined on each transit line, without fixedly assigning communication bandwidths to individual virtual paths and, in respect of the individual transit lines, values of communication bandwidths assigned to virtual channels (VC) which have already been established in virtual paths present on the transit lines are stored. When a request for setting a new call is originated, communication bandwidths of first and second transit lines (10-a, 10-b) on which exists a virtual path to form thereon a virtual channel for the call are checked for their margin enough to accept assignment of a bandwidth requested by the call, the first transit line lying between the cross-connect unit and an originating local switching unit and the second transit line lying between the cross-connect unit and a terminating local switching unit. If the first and second transit lines have a margin enough to accept the assignment of a bandwidth requested by the call, the virtual channel for the call is established on the virtual path and values of communication bandwidths assigned to the first and second transit lines are updated.