1. A focusing device comprising: a distance information acquisition section configured to acquire information on a distance to a subject based on a plurality of image data acquired by taking images of the subject at a plurality of different viewpoint positions; a subject detection section configured to detect a first area and a second area based on the distance information acquired by the distance information acquisition section and threshold information for the distance range within which a subject of interest that obstructs a main subject in the subject is present, the subject of interest being present in the first area in each of the plurality of image data, the subject of interest not being present in the second area; and a focusing estimation section configured to carry out the focusing estimation on the main subject based on the distance information on the second area in each of the plurality of image data.