A phase modulation device comprising: an image data generator configured to generate an image comprising image data corresponding to a distribution of phase change amount or a distribution of phase velocity based on information data; a gradation data generator configured to generate gradation data corresponding to each pixel of the image based on the image data; an adjustment voltage controller configured to generate an adjustment voltage based on the gradation data; and a reflective liquid crystal element to which the gradation data and the adjustment voltage are applied; wherein the reflective liquid crystal element comprises: a pixel region in which a plurality of pixel electrodes are arranged, a driving voltage generator configured to apply a driving voltage corresponding to the gradation data of each pixel to the corresponding pixel electrode so as to generate a sawtooth waveform voltage pattern across the pixel region; and a first adjustment electrode adjacent to the pixel region and extending in a first direction orthogonal to the direction along which each sawtooth of the sawtooth waveform voltage pattern is repeated, the pixel region comprises a plurality of pixel blocks configured to modulate the phase of a signal light incident on the pixel region based on the sawtooth waveform voltage pattern, so as to change the wavefront of the signal light, and the adjustment voltage controller applies to the first adjustment electrode an adjustment voltage having the same voltage value as the driving voltage applied to a pixel electrode of a pixel block adjacent to the first adjustment electrode. an image data generator configured to generate an image comprising image data corresponding to a distribution of phase change amount or a distribution of phase velocity based on information data; a gradation data generator configured to generate gradation data corresponding to each pixel of the image based on the image data; an adjustment voltage controller configured to generate an adjustment voltage based on the gradation data; and a reflective liquid crystal element to which the gradation data and the adjustment voltage are applied; wherein the reflective liquid crystal element comprises: a pixel region in which a plurality of pixel electrodes are arranged, a driving voltage generator configured to apply a driving voltage corresponding to the gradation data of each pixel to the corresponding pixel electrode so as to generate a sawtooth waveform voltage pattern across the pixel region; and a first adjustment electrode adjacent to the pixel region and extending in a first direction orthogonal to the direction along which each sawtooth of the sawtooth waveform voltage pattern is repeated, the pixel region comprises a plurality of pixel blocks configured to modulate the phase of a signal light incident on the pixel region based on the sawtooth waveform voltage pattern, so as to change the wavefront of the signal light, and the adjustment voltage controller applies to the first adjustment electrode an adjustment voltage having the same voltage value as the driving voltage applied to a pixel electrode of a pixel block adjacent to the first adjustment electrode. a pixel region in which a plurality of pixel electrodes are arranged, a driving voltage generator configured to apply a driving voltage corresponding to the gradation data of each pixel to the corresponding pixel electrode so as to generate a sawtooth waveform voltage pattern across the pixel region; and a first adjustment electrode adjacent to the pixel region and extending in a first direction orthogonal to the direction along which each sawtooth of the sawtooth waveform voltage pattern is repeated, the pixel region comprises a plurality of pixel blocks configured to modulate the phase of a signal light incident on the pixel region based on the sawtooth waveform voltage pattern, so as to change the wavefront of the signal light, and the adjustment voltage controller applies to the first adjustment electrode an adjustment voltage having the same voltage value as the driving voltage applied to a pixel electrode of a pixel block adjacent to the first adjustment electrode.