A head drive apparatus of an inkjet printer, having: a plurality of nozzles provided to an inkjet head for ejecting liquid drops; actuators provided corresponding to the nozzles; and a drive unit that applies a drive signal to the actuators, wherein the drive unit, comprising: a drive waveform generator that generates a drive waveform signal as a reference of a signal to control drive of the actuators; a modulator that pulse modulates a drive waveform signal generated by the drive waveform generator; a digital power amplifier that amplifies power of a modulated signal subjected to the pulse modulation by the modulator; a low pass filter that smoothes a amplified digital signal subjected to the power amplification by the digital power amplifier and supplying the signal as a drive signal to the actuators; and an inverse filter provided in a subsequent stage of the drive waveform generator that corrects at least the frequency characteristics of the filter comprised of capacitances of the low pass filter and the actuators to a predetermined frequency characteristics, independently of the number of the actuators to drive.