In accordance with an embodiment, a pattern inspection method includes: applying a light generated from a light source to the same region of a substrate in which an inspection target pattern is formed; guiding, imaging and then detecting a reflected light from the substrate, and acquiring a detection signal for each of a plurality of different wavelengths; and adding the detection signals of the different wavelengths in association with an incident position of an imaging surface to generate added image data including information on a wavelength and signal intensity, judging, by the added image data, whether the inspection target pattern has any defect, and when judging that the inspection target pattern has a defect, detecting the position of the defect in a direction perpendicular to the substrate.