A chest image rotation apparatus includes a chest image input unit that is used to input a chest image, a vertebral-body region extraction unit that extracts a vertebral-body region from the input chest image, a vertebral-body direction calculation unit that calculates, based on the extracted vertebral-body region, the direction of vertebral bodies in the chest image, a chest image rotation unit that rotates the chest image so that the calculated direction of the vertebral bodies becomes perpendicular to the horizontal side of the chest image, and an output unit that outputs the rotated chest image.