Employing a first image and a second image that represent a subject in different phases, based on a first insertion position and a first tip position of the first image and deformation information for deforming the first image so as to be aligned with the second image, a second insertion position of the second image corresponding to the first insertion position and a second tip position are specified such that a direction corresponding to a first insertion direction from the first insertion position toward the first tip position becomes a second insertion direction from the second insertion position toward the second tip position, and a second observation image obtained by visualizing the inside of the subject in a phase corresponding to the second image with the second tip position as a viewpoint is generated. Thereby, observation images of different phases as viewed through a virtual rigid surgical device are generated.
