An index value output circuit outputs an index value in response to a VCI added to the first signaling cell outputted from a terminal unit. A switching data output circuit outputs switching data for determining a path for signaling cells, based on the index value. Hence, by revising the index value according to a congestion state of an ATM switch, the above path is dynamically changed. The same index value is inserted in the second and subsequent signaling cells outputted from the terminal unit. Because switching data are based on the same index value, all signaling cells from the same terminal units are fed to the same signaling terminator.