A processing apparatus is provided that receives and processes an anterior segment three-dimensional image of a subject's eye. The apparatus includes a first SS position specifying unit that accepts identification of at least three SS positions of the subject's eye, using at least two representative images from among two-dimensional tomographic images constituting the three-dimensional image, a true circle calculating unit that calculates a reference true circle passing through the at least three SS positions, and a second SS position specifying unit that identifies the SS positions in non-representative images other than the representative images, based on the reference true circle.