Provided is a mask inspection apparatus including: emitting unit for emitting electron beams onto a sample; electron detecting unit for detecting the quantity of electrons produced, by the emission of the electron beams, from the sample with patterns formed thereon; image processing unit for generating image data for the patterns on the basis of the electron quantity; and controlling unit for controlling the emitting unit, the electron detecting unit, and the image processing unit. The controlling unit calculates, from the size of a designated observation area of the sample, a division number of divisional images that are synthesized to form a joint image that covers the entire designated observation area. The controlling unit determines divisional areas so that adjacent divisional areas partially overlap each other. The controlling unit acquires SEM images for the respective divisional areas. The controlling unit synthesizes the SEM images of the divisional areas on the basis of coordinate data for the divisional areas and on the basis of edge information for patterns included in the overlapping regions, and thereby creates an SEM image of a wide field of view that covers the observation area.