Electron emission from a field emitter array (FEA) was magnified by making use of an emission microscope, and the stability of the individual microtip was examined. The number of observable microtips increased with the total emission current of the whole FEA, and approached 90% of it. Some microtips showed unstable emission and the number of such unstable microtips increased with the total emission current. Gas molecules. which adsorbed locally to inside the microtip, would be caused by the instability of the electron emission.