1. An ion beam work apparatus comprising: ion beam radiation means for focusing and radiating an ion beam extracted from an ion beam source on a target placed on a moving mechanism, and scanning two-dimensionally the ion beam radiation position; secondary particle detection means for detecting secondary particles generated from a surface of said target by radiation of said ion beam, and forming a secondary particle image from the detection signals; display means fopr superposing a display of said secondary particle image near a processing area formed by said secondary particles with a different image having position information not obtained from said secondary particle image and indicating a wiring layer of said target near the processing area, said different image including at least one of an optical microscope image and an image derived from an optical microscope image; first means for detecting a relative deviation of reference points for each of said secondary particle image and said different image, and for moving at least one of said images with respect to the other of said images so that the relative deviation is minimized; second means for setting the processing area of said target based on the position information of said different image as adjusted by said first means; and third means for processing a portion of the wiring layer of said target by radiating the ion beam from said ion beam radiation means on the processing area set by the second means;