To get a transmission sound volume easy to hear at a front entrance slave machine under atmosphere noise such that an automatic-alternate transmission/reception changeover circuit cannot be switched, by making transmission sound volume louder during press-talk operation.

When a master machine 2 is called from a front entrance slave machine 1 and a call switch 27 is pressed down by the master machine 2 with a first press-down mode to drive an automatic-alternate transmission/reception changeover circuit to conduct automatic-alternate changeover for transmission/reception, then a call with hands-free operation is conducted among a microphone 14 in the front entrance slave machine 1, a microphone 23 for which signals are amplified by a speaker 12 and a transmission amplifier 24 in the master machine 2, and a speaker 21 for which signals are amplified by a reception amplifier 22. A CPU 31 of the master machine 2 is equipped with a function for controlling the automatic-alternate transmission/ reception changeover circuit to get a transmission state forcedly and for controlling the transmission amplifier 24 to make the degree of amplification for the transmission amplifier 24 larger and make transmission sound to the front entrance slave machine 1 louder, by pressing down the call switch 27 with a second press-down mode during calling.