A head unit includes an input section that receives control data for controlling the discharging of liquid. The input section includes first and second input sections. First and second control data memorizing sections memorize first and second control data for a first and a second group of nozzles, respectively. Either a first or a second processing step is selectively performed. In the first processing step, first control data inputted from the first input section or the second input section is memorized in the first control data memorizing section, whereas second control data inputted from the same input section is memorized in the second control data memorizing section. In the second processing step, first control data inputted from the first input section is memorized in the first control data memorizing section, whereas second control data inputted from the second input section is memorized in the second control data memorizing section.