PURPOSE: To make a call of high sensitivity possible by preventing a received tone from detouring by using a provided wireless handset, attachable to and detachable to a telephone set, by switching.

CONSTITUTION: Wireless handset 4, attachable to and detachable from telephone set 3, includes antenna 13b, FM transmitter 14, microphone 15, switch 16, and battery 17 and on detachment from telephone set 3, switch 16 turns ON to connect battery 17 to transmitter 14, so that it will be ready for a call. When the vehicle is stopped and handset 6 is left off hook switch 7, switches 8a and 8b are changed over to start an ordinary call by way of mobile station 2 and antenna 1. In driving, on the other hand, handset 6 is placed in an on-hook state and handset 4 is placed closely to the mouth of a driver being left off telephone set 3 to make the call making use of an extremely-weak radio wave, thereby making the call via loudspeaker 11.