An adder unit (60e) reads a desired CGH pattern from a pattern memory unit (60a) and a phase distortion correction pattern from a distortion-correction pattern memory unit (60d) and adds both patterns together to generate a phase distortion corrected pattern. A control unit (60g) controls a phase modulation module (40) in accordance with the phase distortion corrected pattern. Accordingly, phase-modulated light based on the desired phase pattern can be generated precisely, easily and quickly.