1. A pattern inspection apparatus, comprising: an optical image acquiring unit configured to acquire optical image data of a target plate to be inspected, the target plate being formed as a pattern; a design image data generating unit configured to generate design image data based on a design pattern serving as a base of pattern formation of the target plate; and a comparing unit configured to input region image data generated based on information of a region pattern which is input to the pattern inspection apparatus, wherein the information of the region pattern represents a predetermined region and is formed in the same format as that of information of the design pattern, and to compare the optical image data with the design image data based on the region image data, wherein both of the information of the region pattern and the information of the design pattern include, as the format, a coordinate (x, y), a length of side, and a graphic code serving as identifier which discriminates graphic type, and the region image data is generated using the coordinate (x, y), the length of side, and the graphic code included in the information of the region pattern.