A pattern inspection apparatus is designed to quickly and accurately perform an inspection of an inspecting sample, such as masks, wafers or so forth by irradiating electron beams onto the inspection sample and detecting a secondary electron or a backscattered electron reflected from the surface of the inspecting sample or a transmission electron passing through the inspection sample. The pattern inspection apparatus includes an electron beam generating means including at least one electron gun for generating at least one electron beam irradiating on the surface of the inspecting sample, a movable means for supporting the inspecting sample, a detecting means including a plurality of electron detecting elements for detecting electrons containing information related to the construction of the inspection sample and a detection signal processing means for processing simultaneously or in parallel formation the outputs of the electron detecting elements of the detecting means. Also, when a plurality of electron beams are used for simultaneous irradiation of the inspecting sample, the pattern inspection apparatus is provided a mechanism for avoiding interference of a reflected beam of the adjacent electron beam.