PURPOSE: To offer call waiting (CW) for general telephone sets tentatively by disconnecting a path forcibly if a call from a general telephone subscriber to an earth with a rapid call while the path is held and connected to the control line.

CONSTITUTION: A call tone is sent to a general telephone subscriber 101 in the route of a CW device 105-STC 104-channel 103 (path 107) and subscriber line 102 and the subscriber listens to the 2nd call tone. Then the subscriber 101 dials a number decided to be free from the charge. In dialing the number other than unpaid call, the call is cut off forcibly by the function of the SCT. In receiving the number by the exchange, a channel path 108 between the CW device 105 and the test stand 106 is connected and the general telephone subscriber 101 becomes a CW subscriber to attain the talking state with the operator of the test stand 106. Thus, the CW service is executed tentatively to a general telephone call.