A first storage portion stores, in advance, first reference voltage values respectively for ink ejection portions, the first reference voltage values corresponding to a predetermined first image density value. A second storage portion stores, in advance, voltage values that are different from each other, and measurement values that indicate image densities respectively corresponding to the voltage values. A voltage value calculating portion, at a predetermined change timing for changing image density, calculates second reference voltage values respectively for the ink ejection portions based on the voltage values and the measurement values, the second reference voltage values corresponding to a second image density value that is different from the first image density value. A voltage switching portion switches driving voltages that are applied to the ink ejection portions, from driving voltages having the first reference voltage values to driving voltages having the second reference voltage values.