To surely estimate a rib shape photographed in a chest image of the object in a short time.

An object rib shape Ps is extracted from the chest image P obtained by photographing the object. The rib model shape M most similar to the extracted object rib shape is searched from a plurality of rib model shapes M generated using a statistical method based on a plurality of rib shapes Ps of the chest images acquired by photographing, the searched rib model shape M is estimated as the rib shape photographing the object.