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; a reflective liquid crystal element having a pixel region in which a plurality of pixel electrodes are arranged, and 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, wherein the pixel region comprises: a plurality of pixel blocks configured to modulate the phase of an incident signal light based on the voltage pattern so as to change the wavefront of the incident signal light, and a first blank area formed between at least two first pixel blocks among the plurality of pixel blocks and extending in a first direction orthogonal to the direction along which each sawtooth of the sawtooth waveform voltage pattern is repeated, two or more pixel electrodes of the first blank area being arranged in the first direction, and wherein the same driving voltage as the driving voltage applied to one of the pixel electrodes of one of the at least two first pixel blocks is applied to one of the two or more pixel electrodes of the first blank area adjacent to the one of the pixel electrodes of the one of the at least two first pixel blocks. 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; a reflective liquid crystal element having a pixel region in which a plurality of pixel electrodes are arranged, and 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, wherein the pixel region comprises: a plurality of pixel blocks configured to modulate the phase of an incident signal light based on the voltage pattern so as to change the wavefront of the incident signal light, and a first blank area formed between at least two first pixel blocks among the plurality of pixel blocks and extending in a first direction orthogonal to the direction along which each sawtooth of the sawtooth waveform voltage pattern is repeated, two or more pixel electrodes of the first blank area being arranged in the first direction, and wherein the same driving voltage as the driving voltage applied to one of the pixel electrodes of one of the at least two first pixel blocks is applied to one of the two or more pixel electrodes of the first blank area adjacent to the one of the pixel electrodes of the one of the at least two first pixel blocks. a plurality of pixel blocks configured to modulate the phase of an incident signal light based on the voltage pattern so as to change the wavefront of the incident signal light, and a first blank area formed between at least two first pixel blocks among the plurality of pixel blocks and extending in a first direction orthogonal to the direction along which each sawtooth of the sawtooth waveform voltage pattern is repeated, two or more pixel electrodes of the first blank area being arranged in the first direction, and wherein the same driving voltage as the driving voltage applied to one of the pixel electrodes of one of the at least two first pixel blocks is applied to one of the two or more pixel electrodes of the first blank area adjacent to the one of the pixel electrodes of the one of the at least two first pixel blocks.