The disclosure provides a voltage control device for controlling supply voltages of a power amplifier (PA). The voltage control device includes a first processing circuit to provide a first supply voltage to at least one driving stage amplifier of the PA, and a second processing circuit to provide a second supply voltage to an output stage amplifier of the PA. The first supply voltage is generated according to an average-power-tracking (APT) mechanism related to an average power level of a radio frequency (RF) signal transmitted by the PA.