1. An inspection method using an electron beam, comprising the steps of: irradiating a sample on which a pattern is formed with an electron beam; generating an inspection image and a reference image based on a secondary electron or a reflected electron emitted by the sample; determining an abnormal pattern based on a difference in the halftone values in each pixel between the inspection image and the reference image; determining a plurality of feature quantities of the abnormal pattern based on an image of the abnormal pattern; and designating a range for classifying the type of the abnormal pattern based on the distribution of the plurality of feature quantities of the abnormal pattern.