To prevent occurrence of a complicated operation for the manual three-dimensional simulation by performing the switching between a rotational operation and a parallel shift according to change of the dragging speed when a dragging operation is caused by the parallel shift of a mobile object.

A rotation/shift decision part 4 decides a rotational operation or a parallel shift based on the operation contents received from an input part 1. Based on this decision result, the processing is shifted to a coordinate position calculation part 6 and a visual point angle calculation part 5 against the parallel shift and the rotational operation respectively. The part 6 calculates the change of coordinate position of the center of a mobile object, and the part 5 calculates the rotation angle to reflect it on the visual point angle. The three-dimensional coordinate value thus obtained is converted into the two-dimensional coordinate value at a two-dimensional coordinate conversion part 7 and shown at a display part 3. At the same time, the boundary value is set for the dragging speed of a mouse and the rotational operation and the parallel shift are decided by combinations of speed areas and modes.