1. An electron microscope comprising: a main body including an electron beam source, deflectors for scanning the electron beam across a two-dimensional surface of a specimen, and detectors for detecting signals emitted from the specimen in response to the scanned beam; a processor executing a program stored on a hard disk or in RAM such that it stores the signals from the detectors as data representing an electron microscope image of the specimen that includes a plurality of identical patterns, and spectrum data of the specimen corresponding to pixels of the electron microscope image, and such that it extracts from the electron image a plurality of small-area images, each small-area image being identical in size, and having the identical pattern, and such that it reads the spectrum corresponding to pixels of the extracted small-area images and adds up the spectrum at each pixel of the small-area images on a corresponding pixel basis to generate an elemental mapping image of the specimen that corresponds to each of the small-area images.