A computer sets a first point on a first part in a plurality of tomographic images of an organ. The computer determines a relative position of the first point with respect to reference positions of the first part and a second part in the tomographic images. The computer sets a second point in association with the first point, on the first part in a 3D model representing a structure of the organ, such that a relative position of the second point with respect to reference positions of the first part and the second part in the 3D model matches the relative position of the first point. Then, the computer deforms the 3D model such that, when the tomographic images and the 3D model are placed in the same coordinate system, the position of the second point matches that of the first point.