PURPOSE: To shorten connection time by connecting a connectionless type communication network by a VC, automatically deciding a VPI and a VCI by an address processor and performing transfer to a switching element.

CONSTITUTION: The reception data of a net node NT 301 are read in an input side dynamic memory access controller DMAC 103, data are retrieved by the address processors APs 101 and 102 and a CPU 121 is interrupted. The CPU 121 reads a segment address from the AP 102, specifies the port address of the data and sets connection from a port connected to the AP to an output port to a switching unit element SEU 111. Then, data transfer from the AP 102 to the SEU 111 is set to the DMAC 103, the data are read from the output port of the AP 102 and the data are written in the SEU 111 and transferred to an output side NT 301 by an output side port DMAC 103. They are converted into serial data there and sent out to an AT network 150.