PURPOSE: To execute effective communication between a host and a slave telephone sets by transmitting a switching control signal from the slave set, switching a mode from a pulse dial to a tone dial in the host set, and instructing that it is switched to the tone dial in the slave set.

CONSTITUTION: Dial transmission is executed by the pulse dial from the slave set to the master set. If a line is recognized to be connected, the dial mode switching key of a keyboard 18 in the slave set 2 is operated and the switching control signal is transmitted to the host set 11. In the host set 1 which has received the switching signal, a control circuit 10 detects the switching control signal and switches the mode from the pulse dial to the tone dial. The circuit 10 simultaneously transmits to the slave set 2 is signal indicating that the mode has switched to the tone dial, whereby an indicator 19 in the slave set 2 is lighted and it instructs that the mode is switched to the tone dial.