1. A depth measurement apparatus for measuring depth information on a subject by using a plurality of images having different blurs taken under different imaging parameters, the depth measurement apparatus comprising: a spatial frequency determination unit configured to determine a spatial frequency band from spatial frequencies present in at least one of the plurality of images; and an image comparison unit configured to compare the plurality of images by using a component of the spatial frequency band of the plurality of images, and outputs a depth dependence value dependent on a depth of the subject.