PURPOSE: To exactly correct the drop-out defect part of the mask pattern of a mask in a short period of time by projecting an IR laser simultaneously with projection of a UV laser to the above-mentioned defect part of the mask placed in the vapor of a metal compd.

CONSTITUTION: The IR laser 11 is projected simultaneously with the UV laser 8 to the drop-out defect part 3 of the mask pattern 2 in the vapor 7 of the metal compd. The IR laser is provided with the large irradiation angle in such a manner that the peripheral part of the UV laser 8 can be irradiated as well. As a result, the IR laser 11 evaporates the chromium formed by the thermo-CVD reaction in the peripheral part of the irradiation region of the UV laser 8 and, therefore, the chromium 9 is formed only in the region irradiated with the UV laser 8. The drop-out defect part 3 of the pattern 2 is thereby exactly corrected in a short period of time.