1. A depth measurement apparatus for calculating depth information on a subject in an image by using a plurality of images having different blurs taken under different imaging parameters, the apparatus comprising: a region segmentation unit configured to segment at least one of the images into regions based on an image feature amount, wherein in each of the regions pixels are presumed to be substantially equal in depth to the subject; and a depth calculation unit configured to calculate a depth for each region resulting from the segmentation by the region segmentation unit and serving as a processing target region for depth calculation, the depth calculation unit further adapted to set the calculated depth as the depth of the processing target region.