A method of correcting a defective portion of an exposure window in a lithography mask, such as an EPL mask, includes a first step of irradiating a defective portion of the exposure window using a charge particle beam to perform correction processing, and a second step of irradiating another portion of the exposure window with the charged particle beam to eliminate attached matter therefrom, the attached matter consisting of particles ejected from the defective portion of the exposure window as a result of irradiation with the charged particle beam during the first step. The first step and the second step are sequentially repeated N times, wherein N is an integer of 2 or more, to thereby reduce the time needed for eliminating the attached matter.