A defect coordinates measurement method includes a step of detecting detected coordinates of a fiducial mark and a defect of a mask blank placed on support pins, a step of detecting detected coordinates of the alignment mark of a reference mask placed on the support pins, a step of extracting a reference mark near the detected coordinates of the defect among the plurality of reference marks based on the detected coordinates of the defect of the mask blank and the alignment mark of the reference mask, a step of detecting detected coordinates of the extracted reference mark, and a step of calculating coordinates of the defect based on the detected coordinates of the reference mark and the detected coordinates of the defect.