An image acquisition device comprising: a light source for outputting excitation light including a wavelength for exciting a sample; a spatial light modulator having a plurality of pixels two-dimensionally arranged and for modulating a phase of the excitation light for each of the plurality of pixels; an irradiation optical system (15, 16) for radiating the modulated excitation light to the sample, wherein the irradiation optical system includes a first optical system and a first objective lens, and the first optical system includes a lens for focusing the excitation light from the spatial light modulator on the pupil of the first objective lens; a detection optical system for forming an image of detection light emitted from the sample in association with irradiation of the excitation light from the irradiation optical system (15, 16); a photodetector for capturing the image of the detection light formed by the detection optical system; a control unit for controlling an amount of phase modulation for each of the plurality of pixels in accordance with a phase pattern in which phase values corresponding to the plurality of pixels are two-dimensionally distributed, wherein the phase pattern is a phase pattern generated based on a predetermined basic phase pattern, the basic phase pattern includes a first region in which the phase value continuously increases in a predetermined direction and a second region in which the phase value continuously decreases in the predetermined direction and facing the first region in the predetermined direction, the basic phase pattern is non-axisymmetric with respect to a straight line passing through a center in the predetermined direction and orthogonal to the predetermined direction, and an absolute value of a gradient of a phase value in the first region is different from an absolute value of a gradient in the second region, thereby enabling the spatial light modulator to generate sheet-like excitation light. a light source for outputting excitation light including a wavelength for exciting a sample; a spatial light modulator having a plurality of pixels two-dimensionally arranged and for modulating a phase of the excitation light for each of the plurality of pixels; an irradiation optical system (15, 16) for radiating the modulated excitation light to the sample, wherein the irradiation optical system includes a first optical system and a first objective lens, and the first optical system includes a lens for focusing the excitation light from the spatial light modulator on the pupil of the first objective lens; a detection optical system for forming an image of detection light emitted from the sample in association with irradiation of the excitation light from the irradiation optical system (15, 16); a photodetector for capturing the image of the detection light formed by the detection optical system; a control unit for controlling an amount of phase modulation for each of the plurality of pixels in accordance with a phase pattern in which phase values corresponding to the plurality of pixels are two-dimensionally distributed, wherein the phase pattern is a phase pattern generated based on a predetermined basic phase pattern, the basic phase pattern includes a first region in which the phase value continuously increases in a predetermined direction and a second region in which the phase value continuously decreases in the predetermined direction and facing the first region in the predetermined direction, the basic phase pattern is non-axisymmetric with respect to a straight line passing through a center in the predetermined direction and orthogonal to the predetermined direction, and an absolute value of a gradient of a phase value in the first region is different from an absolute value of a gradient in the second region, thereby enabling the spatial light modulator to generate sheet-like excitation light.