1. A circuit pattern inspecting apparatus, which detects secondary electrons or back scattering electrons generated by irradiating an electron beam on a substrate having a circuit pattern formed thereon and detects an abnormality of said circuit pattern, comprising: an image processing unit for generating an acquired image based on an intensity of a signal of said detected secondary electrons or back scattering electrons, and generating a reference image by removing a noise component from said acquired image; and a control unit for extracting said noise component included in said acquired image based on a comparison of the acquired image with the reference image, and performing a frequency analysis on said extracted noise component.