1. A pattern inspection device, comprising: an image picking-up portion for picking up an image of a pattern formation member in which a plurality of opening patterns are formed so as to obtain a picked-up image of the pattern formation member; a reference image obtaining portion for obtaining a reference image used for comparing with the picked-up image; a first center location detecting portion for detecting center locations of a plurality of opening pattern images included in the picked-up image; a second center location detecting portion for detecting center locations of a plurality of opening pattern images included in the reference image; a first summation calculation portion for calculating a summation of gradation values about regions predetermined by using the center locations of the picked-up image detected by the first center location detecting portion as a criterion; a second summation calculation portion for calculating a summation of gradation values about regions predetermined by using the center locations of the reference image detected by the second center location detecting portion as a criterion; and a summation comparing portion for calculating differences between the summation of gradation values obtained by the first summation calculation portion and the summation of gradation values obtained by the second summation calculation portion, and detecting defects for the opening pattern based on the calculation result.