PURPOSE: To call a principal to use a specific push-button telephone set by carrying the slave set of a cordless telephone set when a call is placed to the specific push-button telephone set by placing the call simultaneously to the cordless telephone set whose slave set is portable.

CONSTITUTION: When the cordless telephone set 6 is connected to a main device 1 as a reference telephone terminal and the call to the specific push-button telephone sets 2-5 is performed, a means 19 to set the function of the cordless telephone set 6 as a simultaneous call telephone set to be called simultaneously is provided, and when the call to the specific push-button telephone sets 2-5 is placed, the call is also placed to the cordless telephone set 6 simultaneously. Thereby, it is possible to call the principal to use the push-button telephone set without necessitating the designation of a call destination especially by carrying the slave set of the cordless telephone set 6 when the user quits from a place where the push-button telephone set is installed.