PURPOSE: To adjust a speech loss for each transmission route by deciding the speech loss based on a combination table between caller numbers and a called numbers.

CONSTITUTION: In the case of dialing from a subscriber terminal equipment 1 to an extension terminal equipment 13, set up information (SETUP) is sent from an ISD network 2 to a PBX (private branch of exchange) 3 as incoming information. The PBX 3 extracts a caller number and a called number of the extension terminal equipment being a final destination number from the setup information to select a transmission route. Two transmission routes R1, R2 are in existence in this case. When the transmission route R1 is selected, an index table is referenced based on a destination called number dialed from a trunk 5 to decide a speech loss and the loss is inserted to the route. Furthermore, a PBX 7 inserts a speech loss to attain talking with the extension terminal equipment 13 based on the setup information received from a trunk 9 an connects the route.