According to one embodiment, a method of correcting defects in a reflection-type mask is provided, which comprises acquiring a mask-pattern image of the mask, by using a mask-defect correction apparatus includes a mechanism configured to detect a defect in the mask and a mechanism configured to correct the defect, acquiring a simulated wafer-transfer optical image for the mask, by using an AIMS configured to simulate a wafer-transfer optical image, thereby to determine whether the mask is defective, locating a mask defect, in a mask-pattern image acquired by the mask-defect correction apparatus, by referring to the simulated pattern image acquired by the AIMS, and correcting the defect by the mask-defect correction apparatus, on the basis of the position of the mask defect, thus detected.