A photomask defect correction method for correcting a defect of a photomask. A defect in a portion of a photomask to be corrected is observed and information of the observed defect for performing correction of the defect is acquired. The observed defect is corrected in accordance with the acquired defect information by irradiating the observed defect with a focused ion beam from an ion beam irradiation system having a gas field ion source that generates rare gas ions for forming the focused ion beam.