1. A pattern inspection apparatus comprising: a first stage configured to mount a target object to be inspected on which a pattern is formed and which is located at a position displaced from a gravity center of the first stage; a first two-dimensional scale and a second two-dimensional scale arranged to be on the first stage and opposite each other with respect to a position of the gravity center of the first stage; a second stage arranged to be under a region overlapping with the gravity center of the first stage and not overlapping with the target object mounted on the first stage, and configured to support and move the first stage; a calculation processing circuitry configured to calculate a position of the target object to be inspected, using position information measured by the first two-dimensional scale and the second two-dimensional scale; an illumination optical system configured to illuminate the target object to be inspected, with an inspection light; a sensor configured to capture an optical image of the pattern formed on the target object to be inspected, in a state where the first stage on which the target object to be inspected is mounted is moving; and a comparison processing circuitry configured to compare, for each pixel, the optical image with a reference image corresponding to the optical image.