A pattern inspection apparatus includes an optical image acquiring unit that acquires optical image data of a target plate formed as a pattern. The pattern inspection apparatus also includes a design image data generating unit that generates first design image data based on a first design pattern serving as a base of pattern formation of the target plate. The pattern inspection apparatus additionally includes a comparing unit that compares the optical image data and the first design image data with each other. Further, information of a second design pattern is input in parallel with information of the first design pattern to the pattern inspection apparatus. In the comparing unit, second design image data generated based on the second design pattern is further input, and the optical image data is compared with the second design image data in place of the first design image data.