The present invention provides a frequency multiplier apparatus. The frequency multiplier apparatus includes an injection-locked frequency multiplier and a frequency-to-control signal converter. The injection-locked frequency multiplier outputs an output signal having a first frequency in response to an input signal having a first basic frequency. The frequency-to-control signal converter provides a first control signal to the injection-locked frequency multiplier in response to the input signal. The injection-locked frequency multiplier adjusts the first frequency to a second frequency in response to a change of the first control signal when the first basic frequency is changed to a second basic frequency.