Abstract: An instruction point is movably provided in a three-dimensional space and can be freely moved by a finger tip of an operator. When the operator moves the instruction point to a desired position in the three-dimensional space and selects an arbitrary point, a three-dimensional position of the instruction point is measured and is input to a three-dimensional input apparatus. An image object is displayed in the three-dimensional space on the basis of image object information which has been previously stored. A check is made to determine whether or not the instruction point is virtually in contact with the virtual object in the three-dimensional space on the basis of the virtual object information and the position information of the instruction point.