Provided is a power supply circuit capable of operating with low noise and low power consumption. In a power supply circuit, a power level control signal Pa for controlling a power level of a power amplifier, and an internal current control signal Pb which is a result of smoothing the power level control signal Pa at predetermined time intervals, are inputted to an operational amplifier. The operational amplifier amplifies the power level control signal Pa, and controls an internal current thereof such that the internal current has a similar characteristic to that of the internal current control signal Pb. A power transistor amplifies an output of the operational amplifier, and supplies a voltage to the power amplifier.