A phase-modulating apparatus includes a spatial light modulator, an input value setting unit, a plurality of sets of reference data, a converting unit, and a driving unit. The input value setting unit sets an input value for each pixel. Each set of reference data corresponds to at least one pixel. The converting unit converts an input value inputted for each pixel to a control value by referencing the corresponding set of reference data. The driving unit converts the control value to a voltage value. The driving unit drives each pixel with a drive voltage corresponding to the voltage value. Each set of reference data correlates a plurality of first values from which input values are taken, and a plurality of second values from which control values are taken to ensure that the relationship between the plurality of first values and phase modulation amounts attained by the corresponding at least one pixel is a prescribed linear relationship.