To enable mutual communication between different kinds of terminals contained in each system and to allow only a multi-function exchange to provide data communications including low-speed sound communication upto high-speed, high quality data transmission.

This device is composed of a main device equipped with an ATM cell relay system switch 10 and a control part 20, plural terminal interface units 11 to 15 contained in the main device, and plural line interface units 16 to 19, wherein at least one ATM buses 22 are connected to the terminal interface. As a control signal path between the terminal interface units 11 to 15, the line interface units 16 to 19 and the control part 20, a permanent virtual circuit(PVC) is provided, and a private cell by way of the PVC controls the interface units 11 to 19.