PURPOSE: To minimize the number of blocks at selecting a route and to reduce division losses of a track with respect to the same route by giving commonly the information for showing which route of each processor is idle to each processor or a shared memory.

CONSTITUTION: A dialing number from a subscriber SUB.0 is received in a terminal system ETS0, and a dial receiving is executed by a processor through a subtrunk SUB.T and a switch SW. After it is analyzed and the route selection is executed, a trunk of the route is caught, and idle and busy displays in correspondence to trunks in memory in a terminal processor and displayed and set in an idle/busy display area A of a common memory device CM. When a route through a digital switching processor is selected because of no output route of a self terminal system in the terminal processor, a high order digital switching processor checks the idle and busy displays in correspondence to the terminal processor of the common memory. When it is the idle display, the contained terminal processor is selected. In case of the busy display, the terminal processor displayed idle is selected.