A perspective transformation is performed to a three-dimensional model and a model coordinate system indicating a reference attitude of the three-dimensional model to produce a projection image expressing a relationship between the model and the model coordinate system, and a work screen is started up. A coordinate of an origin in the projection image and rotation angles of an X-axis, a Y-axis, and a Z-axis are displayed in work areas on the screen to accept a manipulation to change the coordinate and the rotation angles. The display of the projection image is changed by a manipulation. When an OK button located is pressed, the coordinate and rotation angle are fixed, and the model coordinate system is changed based on the coordinate and rotation angle. A coordinate of each constituent point of the three-dimensional model is transformed into a coordinate of the post-change model coordinate system.