A transmitter of a mobile communication terminal including a transmission signal processor for receiving a data signal to be transmitted, modulating the data signal into a radio signal, and outputting the radio signal. A local oscillator device provides the transmission signal processor with a local oscillator signal and a modem for outputs a control signal to power on the transmission signal processor and the local oscillator device when a voice signal is input through a microphone. A delay device for delays the control signal from the modem and provides the transmission signal processor with the delayed control signal.