To prevent transmission from being started erroneously due to noise or the like in the reception of a signal of other station for a voice transmission start circuit in a radio equipment.

A voltage at an L-level (0V) is applied to an NSQ terminal during reception of a signal of other station, and a 0V is applied to a collector of a transistor(TR) 31, then a voltage Vcc is applied to the collector of a TR 30 and the base of a FET 29. Thus, the source and the drain of the FET 29 are conductive, and a voltage between input resistors 4, 5 is fixed to Vcc/2. Thus, independently of the magnitude of the signal given to a microphone 1, an output of an operational amplifier 33 is fixed to Vcc/2, the signal is peak- detected and given to a central arithmetic processing unit 36. In the central arithmetic processing unit 36, the A/D-converted voltage is detected, and since the voltage is always lower than a preset threshold voltage, the transmission start by vice is not caused during the reception of a signal of other station.