There is provided a main subject determining apparatus. A subject detecting unit detects a plurality of subjects from a first image. An obtaining unit obtains posture information of each of the plurality of subjects. For each of the plurality of subjects, a calculating unit calculates, on the basis of the posture information of the subject, a reliability corresponding to a likelihood that the subject is a main subject in the first image. A determining unit determines the main subject of the first image from among the plurality of subjects on the basis of the plurality of reliabilities calculated for the plurality of subjects.