Provided are a mask inspection apparatus and a mask inspection method that can prevent a reduction in a reflectance of a drop-in mirror, which is caused by carbon contaminants. A mask inspection apparatus according to the present invention includes a drop-in mirror including multi-layer film and a reflective surface. The drop-in mirror is configured to reflect illumination light incident on the reflective surface and illuminate the mask. An area of the reflective surface is configured to be greater than an area of an illuminated spot irradiated with the illumination light on the reflective surface. The drop-in mirror is configured to be movable. A position of the illuminated spot on the reflective surface is configured to be moved when the drop-in mirror is moved.