1. A method of inspecting a mask which has a lithographic pattern thereon, comprising the steps of: depositing an electron-emissive layer on a front surface of said mask on which said pattern is formed, said electron-emissive layer emitting electron beams when a rear surface of said mask is irradiated with energy beams; applying said energy beams to said electron-emissive layer through said rear surface of said mask to cause said electron beams to emit from said electron-emissive layer; guiding said electron beams emitted from said electron-emissive layer to an electron optical system, thereby forming an electron beam image of said pattern on a detector means; detecting said electron beam image by said detector means to generate detection signals; and comparing said detection signals corresponding to said pattern with reference signals representing a desirable shape and size of said pattern, thereby to inspect said mask.