A head unit control circuit controls a head unit. The head unit includes an ejector, a determination circuit, and an ejection limit circuit. The ejector includes a displaceable piezoelectric element for controlling the liquid ejection. The piezoelectric element is displaced by changing a drive signal potential. The determination circuit determines whether the piezoelectric element has a predetermined electrical storage capability. The ejection limit circuit stops the drive signal to limit the ejection of the liquid based on the determination. The head unit control circuit includes: a first terminal that outputs an instruction signal instructing the head unit to execute the determination; a second terminal that outputs the drive signal; and a third terminal that is between the first terminal and the second terminal. The third terminal has a smaller potential change width than the second terminal when the ejecting section ejects the liquid.