1. A method for inspecting a flat panel, the method comprising: arranging a camera at a measurement location of the flat panel by horizontally moving at least one of the flat panel and the camera; automatically focusing the camera by using an automatic focusing module having a repeatability distance range on a target to be measured of the flat panel at the measurement location; acquiring a plurality of images of the target to be measured by vertically moving the focused camera upward or downward within a set movement distance range, wherein each of the plurality of images is taken by the camera within a photographing distance range; selecting an image with the highest definition among the plurality of acquired images to process the selected image; and determining whether the target to be measured is defective or not, wherein the set movement distance range for acquiring the plurality of images is greater than the repeatability distance range of the automatic focusing module, and the photographing distance range is smaller than the repeatability distance range of the automatic focusing module.