1. A composition determination device comprising: subject detection means configured to detect a subject in an image based on acquired image data; actual subject size detection means configured to detect the actual size which can be viewed as being equivalent to actual measurements, for each subject detected by said subject detection means; 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; and composition determination means configured to determine a composition with only relevant subjects, distinguished by said subject distinguishing means, as objects.