An inspection apparatus and method comprising a unit for acquiring an optical image of an object to be inspected by irradiating the object with light, wherein the unit includes a line sensor comprising a plurality of sensors linearly arranged in a row, a generating unit for generating a reference image from design data of the object to be inspected, a comparing unit for comparing the optical image with the reference image, a unit for storing data of three lines acquired by the line sensor, and calculating differences between a gradation value of a pixel on a center line and each gradation value of the eight pixels adjacent to the pixel determining if the pixel is a defect if all of the eight differences of the adjacent pixels are more than a predetermined threshold.