A computer aided work support system having a measuring unit for measuring the position and orientation of the measuring unit itself; an image pickup unit for picking up an object to be measured; an unit for generating an estimated image of the object in accordance with information of the form, position, and orientation of the object, the position and orientation of the measuring unit, the position and orientation of the image pickup unit relative to the measuring unit, a plurality of image magnification factors, and the position of the optical axis of the image pickup unit on the screen of a display unit, the display unit displaying the picked-up image and estimated image of the object in a superposed manner at the same time; and a modifying unit for modifying the information of the previous positions and orientations of the object and image pickup unit in accordance with a displacement amount of the estimated image from the picked-up image.