A transmitting circuit, which includes a power amplifier, a processing circuit, and a signal strength indicator circuit. The power amplifier is configured to amplify an input signal according to a power gain of the power amplifier to generate an output signal. The processing circuit is configured to adjust the power gain according to an indicating signal. The signal strength indicator circuit has a plurality of power detection ranges. The signal strength indicator circuit is configured to uses one of the plurality of power detection ranges to detect a power of the output signal to generate the indicating signal.