1. A depth measurement apparatus for measuring depth information on a subject using a plurality of images having different blurs taken under different imaging parameters, the depth measurement apparatus comprising: a region selection unit configured to select image regions including a processing target region from the plurality of images and to output the image regions as region selection images; a spatial frequency determination unit configured to determine a spatial frequency band from spatial frequencies present in at least one of the region selection images; and an image comparison unit configured to compare the plurality of images using a component of the spatial frequency band of the region selection images, and to output a depth dependence value dependent on a depth of the subject in the processing target region, wherein the spatial frequency determination unit is configured to transform the region selection images of the plurality of images into frequency space images, to determine a characteristic frequency band serving as the spatial frequency band present in the region selection images for at least one of the plurality of images, and to select the spatial frequency band used for outputting of the depth dependence value such that the characteristic frequency band is included in the spatial frequency band.