PURPOSE: To select one line among the plural lines capable of performing transmission to a discriminated transmission destination based on the data characteristics of a hierarchy higher than a specified hierarchy by discriminating the transmission destination of a data frame based on the transmission destination identification information of the specified hierarchy among the plural hierarchies.

CONSTITUTION: By the information for respective transmission functions of virtual discrimination VPI and virtual channel discrimination VRI of a user network interface UNI in the data frame of an ATM cell, communication to which the cell belongs is discriminated and user information is discriminated by a payload PT. An information field AAL is constituted of a header, the payload and a trailer and the destination of the cell is specified by the transmission destination address DA of the payload. Also, by the data DEST in the header of a TCP layer higher than an AAL layer, the level of security required for the data frame is judged. In the case of detecting the DEST of the TCP included in the received ATM cell in an address processor 102, a CPU 121 selects the output line of the appropriate security from the features of the respective lines stored in a RAM 123 and sets it in an SEU 111.