To provide a call connection method and a call center system for leveling between a tone volume of an RBT (Ring Back Tone) signal transmitted from a public switched telephone network during calling at call connection start and a speech tone volume during call connection.

The call connection method adopted by the call center system for applying a call connection of a subscriber telephone set to an extension telephone set contained in a private branch exchange via the public switched telephone network wherein the RBT signal is supplied to a speech line leading to a caller during calling of a called party, shuts off the speech line in response to a call connection request wherein the subscriber telephone set is the called party and the extension telephone set is the caller, calls the called party, supervises start of the supply of the RBT signal, generates a pseudo RBT signal at a prescribed tone volume level when detecting the start of supply of the RBT signal, supplies the pseudo RBT signal to the caller, stops the supply of the pseudo RBT signal in response to a reply signal from the called party, and releases the shut-off of the speech line.