A head drive unit comprising: an inkjet head driven based on a drive signal; and a head drive apparatus that outputs a discharge signal to the inkjet head based on image data and a print timing signal that are input from an external apparatus, and discharges a droplet from a nozzle to form an image on a recording medium, wherein the head drive apparatus comprises: a drive signal output unit for outputting the discharge signal used for discharging a droplet from the nozzle to form an image and a meniscus oscillation signal used for an oscillating meniscus at a tips of the nozzle without discharging a droplet from the nozzle as a drive signal to the inkjet head; a cycle generation unit for generating a cyclic oscillation timing signal for the meniscus oscillation signal; an input interruption detection unit for detecting that no input is made and input of the print timing signal is interrupted even though a preset time has elapsed by monitoring input of the print timing signal; and a drive signal selection unit, which is configured to selecting the meniscus oscillation signal as the drive signal output from the drive signal output unit and continuously applying the meniscus oscillation signal to all the nozzles of the inkjet head in synchronization with the oscillation timing signal when the input interruption detection unit. detects that input of the print timing signal has been interrupted, characterised in the the head drive unit is so configured that when a carriage is present in the image forming region, the meniscus in each nozzle is oscillated by interposing the meniscus oscillation signal before or after the print timing signal. an inkjet head driven based on a drive signal; and a head drive apparatus that outputs a discharge signal to the inkjet head based on image data and a print timing signal that are input from an external apparatus, and discharges a droplet from a nozzle to form an image on a recording medium, a drive signal output unit for outputting the discharge signal used for discharging a droplet from the nozzle to form an image and a meniscus oscillation signal used for an oscillating meniscus at a tips of the nozzle without discharging a droplet from the nozzle as a drive signal to the inkjet head; a cycle generation unit for generating a cyclic oscillation timing signal for the meniscus oscillation signal; an input interruption detection unit for detecting that no input is made and input of the print timing signal is interrupted even though a preset time has elapsed by monitoring input of the print timing signal; and a drive signal selection unit, which is configured to selecting the meniscus oscillation signal as the drive signal output from the drive signal output unit and continuously applying the meniscus oscillation signal to all the nozzles of the inkjet head in synchronization with the oscillation timing signal when the input interruption detection unit. detects that input of the print timing signal has been interrupted, characterised in the the head drive unit is so configured that when a carriage is present in the image forming region, the meniscus in each nozzle is oscillated by interposing the meniscus oscillation signal before or after the print timing signal.