Coordinate values of an object located in a coordinate space are stored in a memory. The coordinate space is represented by a first direction, a second direction and a third direction each different. The coordinate values include first coordinate values along the first direction, second coordinate values along the second direction and third coordinate values along the third direction. A stereoscopic image of the object having a parallax along one of the first direction and the second direction is displayed. A direction of the parallax is detected. When the direction of the parallax is the first direction, the first coordinate values are subjected to a parallel projection. When the direction of the parallax is the second direction, the second coordinate values are subjected to the parallel projection.