PURPOSE: To facilitate the test for a terminal equipment by switching an LSI for layer as a terminal equipment for a layer of a network terminator, and selecting the use of software for the terminal equipment into the use of the software for an artificial network terminator.

CONSTITUTION: In the case of use of an artificial network terminator, it is normally possible to set an LSI of a layer 1 as a terminal equipment to an LSI of a layer 1 as a network terminator by a switch command. Thus, an LSI 5 of a layer 1 as a terminal equipment is selected to an LSI of a layer 1 as a network terminator, a transformer 6 as a terminal equipment connecting to an ISDN line is switched to a 1st transformer 4 and the use of a software operated as a terminal equipment is switched to the use of a software 3 for an artificial terminator. Thus, when a switching command is issued, the use of the artificial network terminator is attained and the test of the terminal equipment connecting to an S bus is easily conducted without a trouble.