A depth acquisition device, comprising: a memory; and a processor, wherein the processor performs: acquiring timing information indicating a timing at which a light source irradiates a subject with infrared light by continuous imaging at a predetermined frame rate; acquiring an infrared light image stored in the memory, the infrared light image being generated by a camera mounted on a moving body by imaging a scene including the subject with the infrared light according to the timing indicated by the timing information; acquiring a visible light image stored in the memory, the visible light image being generated by imaging a substantially same scene as the scene of the infrared light image, with visible light from a substantially same viewpoint as a viewpoint of the imaging the infrared light image at a substantially same time as an imaging time of imaging the infrared light image; wherein the imaging is performed at different timings in a frame cycle; detecting a dust region showing dust from the infrared light image; and estimating a depth of the dust region based on the infrared light image, the visible light image, and the dust region, characterized in that in the detecting of the dust region, the processor performs detecting, as the dust region, a higher luminance region having a luminance not less than a first threshold in the infrared light image, when the higher luminance region satisfies a first condition, the first condition being that a center of gravity of the higher luminance region is located on a straight line or an arc, the straight line or the arc intersecting (i) a center of gravity of each of at least two higher luminance regions other than the higher luminance region in the infrared light image and (ii) a Focus of Expansion of one of the infrared light image and the visible light image. a memory; and a processor, wherein the processor performs: acquiring timing information indicating a timing at which a light source irradiates a subject with infrared light by continuous imaging at a predetermined frame rate; acquiring an infrared light image stored in the memory, the infrared light image being generated by a camera mounted on a moving body by imaging a scene including the subject with the infrared light according to the timing indicated by the timing information; acquiring a visible light image stored in the memory, the visible light image being generated by imaging a substantially same scene as the scene of the infrared light image, with visible light from a substantially same viewpoint as a viewpoint of the imaging the infrared light image at a substantially same time as an imaging time of imaging the infrared light image; wherein the imaging is performed at different timings in a frame cycle; detecting a dust region showing dust from the infrared light image; and estimating a depth of the dust region based on the infrared light image, the visible light image, and the dust region, characterized in that in the detecting of the dust region, the processor performs detecting, as the dust region, a higher luminance region having a luminance not less than a first threshold in the infrared light image, when the higher luminance region satisfies a first condition, the first condition being that a center of gravity of the higher luminance region is located on a straight line or an arc, the straight line or the arc intersecting (i) a center of gravity of each of at least two higher luminance regions other than the higher luminance region in the infrared light image and (ii) a Focus of Expansion of one of the infrared light image and the visible light image. acquiring timing information indicating a timing at which a light source irradiates a subject with infrared light by continuous imaging at a predetermined frame rate; acquiring an infrared light image stored in the memory, the infrared light image being generated by a camera mounted on a moving body by imaging a scene including the subject with the infrared light according to the timing indicated by the timing information; acquiring a visible light image stored in the memory, the visible light image being generated by imaging a substantially same scene as the scene of the infrared light image, with visible light from a substantially same viewpoint as a viewpoint of the imaging the infrared light image at a substantially same time as an imaging time of imaging the infrared light image; wherein the imaging is performed at different timings in a frame cycle; detecting a dust region showing dust from the infrared light image; and estimating a depth of the dust region based on the infrared light image, the visible light image, and the dust region, characterized in that in the detecting of the dust region, the processor performs detecting, as the dust region, a higher luminance region having a luminance not less than a first threshold in the infrared light image, when the higher luminance region satisfies a first condition, the first condition being that a center of gravity of the higher luminance region is located on a straight line or an arc, the straight line or the arc intersecting (i) a center of gravity of each of at least two higher luminance regions other than the higher luminance region in the infrared light image and (ii) a Focus of Expansion of one of the infrared light image and the visible light image.