1. A composition determination device comprising: subject detection means configured to detect a subject in an image based on acquired image data, and to determine a predetermined attribute relating to the difference in size of each detected subject, in actual measurements; subject distance detection means configured to detect a subject distance for each subject detected by said subject detection means; subject size detection means configured to detect an in-image size which is the size of the subject in said image, for each subject detected by said subject detection means; actual subject size detection means configured to detect an actual size which can be viewed as being equivalent to actual measurements, for each subject detected by said subject detection means using at least said subject distance and said in-image size; subject distinguishing means configured to distinguish relevant subjects from subjects detected by said subject detection means, based on determination regarding whether or not the actual size detected by said actual subject size detection means is an appropriate value corresponding to a relevant subject after having been corrected using a coefficient corresponding to said determined attribute; and composition determination means configured to determine a composition with only relevant subjects, distinguished by said subject distinguishing means, as objects, the composition being determined by shifting a first image frame along a plane corresponding to the plane of the image to set a new image frame in which the relevant subjects are disposed approximately in the middle of the new image frame.