A head unit to be installed in a liquid ejection apparatus, the head unit comprising: a head module comprising (i) a nozzle plate comprising an ejection surface defining an ejection opening, (ii) a liquid-passage defining member comprising a liquid passage communicating with the ejection opening, the liquid-passage defining member and the nozzle plate being stacked on each other in a stacking direction orthogonal to the ejection surface, (iii) a drive element configured to eject liquid from the ejection opening, and (iv) an interconnect member connected to the drive element; a circuit board connected to the interconnect member; and wherein the nozzle plate comprises: a first end and a second end spaced apart from each other in a first direction that is orthogonal to the stacking direction and that is along the ejection surface; and a third end and a fourth end spaced apart from each other in a second direction that is orthogonal to each of the stacking direction and the first direction and that is along the ejection surface, wherein a distance between the first end and the second end of the nozzle plate is greater than a distance between the third end and the fourth end of the nozzle plate, wherein the circuit board comprises: a fifth end and a sixth end spaced apart from each other in the first direction; and a seventh end and an eighth end spaced apart from each other in the stacking direction, and wherein a distance between the seventh end and the eighth end of the circuit board is greater than a distance between the fifth end and the sixth end of the circuit board, characterised in that the head unit comprises a casing connected to the head module and defining an accommodation space for accommodating the circuit board, and in that the circuit board is disposed in the accommodation space such that a main surface of the circuit board extends along the stacking direction and the first direction. a head module comprising (i) a nozzle plate comprising an ejection surface defining an ejection opening, (ii) a liquid-passage defining member comprising a liquid passage communicating with the ejection opening, the liquid-passage defining member and the nozzle plate being stacked on each other in a stacking direction orthogonal to the ejection surface, (iii) a drive element configured to eject liquid from the ejection opening, and (iv) an interconnect member connected to the drive element; a circuit board connected to the interconnect member; and wherein the nozzle plate comprises: a first end and a second end spaced apart from each other in a first direction that is orthogonal to the stacking direction and that is along the ejection surface; and a third end and a fourth end spaced apart from each other in a second direction that is orthogonal to each of the stacking direction and the first direction and that is along the ejection surface, a first end and a second end spaced apart from each other in a first direction that is orthogonal to the stacking direction and that is along the ejection surface; and a third end and a fourth end spaced apart from each other in a second direction that is orthogonal to each of the stacking direction and the first direction and that is along the ejection surface, wherein a distance between the first end and the second end of the nozzle plate is greater than a distance between the third end and the fourth end of the nozzle plate, wherein the circuit board comprises: a fifth end and a sixth end spaced apart from each other in the first direction; and a seventh end and an eighth end spaced apart from each other in the stacking direction, and a fifth end and a sixth end spaced apart from each other in the first direction; and a seventh end and an eighth end spaced apart from each other in the stacking direction, and wherein a distance between the seventh end and the eighth end of the circuit board is greater than a distance between the fifth end and the sixth end of the circuit board, characterised in that the head unit comprises a casing connected to the head module and defining an accommodation space for accommodating the circuit board, and in that the circuit board is disposed in the accommodation space such that a main surface of the circuit board extends along the stacking direction and the first direction.