An instruction input that permits convenient input of instructions for moving an object in three-dimensional space. A desired instruction is entered by an input device and displayed on the screen of a display device. The instruction specifies at least one position change and one attitude change of the object. A cursor generator displays a cursor showing the position and the attitude of the object. A cursor controller specifies a post-motion position and a post-motion attitude of the main cursor according to the entered instruction. The cursor controller forms a mathematical projection of the main cursor onto a plane based on the specified post-motion position and the specified post-motion attitude of the main cursor which is displayed on the display device to show the post-motion position and post-motion attitude of the object after the desired motion specified by the instruction.