There is provided a method of high-sensitively detecting both of a phase defect existing in a mask blank and a phase defect remaining after manufacturing an EUVL mask. When the mask blank is inspected, EUV light having illumination NA to be within an inner NA but a larger value is irradiated. When the EUVL mask is inspected, by using a dark-field imaging optical system including a center shielding portion for shielding EUV light and a linear shielding portion for shielding the EUV light whose width is smaller than a diameter of the center shielding portion, the center shielding portion and the linear shielding portion being included in a pupil plane, the EUV light having illumination NA as large as or smaller than the width of the linear shielding portion is irradiated.