A frequency shift-keying reader circuit includes a band-pass filter, a low noise amplifier, a first balun, an injection-lock divide-by-2 frequency divider, a sub-harmonic mixer and a low-pass filter. The band-pass filter performs a filtering procedure to a radio frequency signal, wherein the filtered radio-frequency signal is received by the low noise amplifier to provide an injection signal, and the injection signal is received by the first balun to generate a first differential signal and a second differential signal. The injection signal is received by the injection-lock divide-by-2 frequency divider to provide a first oscillation signal and a second oscillation signal, wherein the first differential signal, the second differential signal, the first oscillation signal and the second oscillation signal are received by the sub-harmonic mixer for performing a mixing procedure and thereafter generating an output signal, the low-pass filter performs a filtering procedure to the output signal.