To attain high speed and high efficiency for hop by hop transfer by enhancing a throughput of the hop by hop transfer between an asynchronous transmission mode ATM switch unit and an IP processing unit.

An ATM switch unit 20 is provided with an ATM disassembly/ assembly circuit 13a, which reconfigures an ATM cell requiring hop by hop transfer into an IP packet. The IP packet is transferred to an IP processing unit 10, which retrieves a transfer destination. Furthermore, the IP packet whose transfer destination is retrieved by the IP processing unit 10 is transferred to the ATM switch unit 20 in only a form that Tag information is added to the IP packet, this IP packet is given to the ATM disassembly/assembly circuit 13a, where the IP packet is disassembled into an ATM cell, a virtual channel VC value is acquired based on the Tag information and the disassembled ATM cell is transmitted to a downstream channel from an output port corresponding to the VC value.