PURPOSE: To provide an electron beam source which generates an electron beam having a narrow energy width and which can favorably be used in forming a high performance, milti-funstional electron beam application device using a monochromatic electron beam by selecting a specific electron beam source.

CONSTITUTION: An electron beam source is selected which has a double barrier type quantum well layer and which is structured so that the electron transmission probability of the double barrier layer including the quantum well layer becomes approx. one. Preferably, the double barrier layer is structured so that the electron permiation lengths into the two barrier layers are identical substantially. For example, a barrier layer 12 of a single crystal AlAs film with a film thickness less than the permeation length of electron wave is grown by a molecular beam epitaxy method on the surface of a needle 11 which is made of n+ type GaAs single crystal and whose radius of curvature at the tip is 0.1μm, and thereover a quantum well layer 13 of a single crystal GaAs film is grown, and thereby an electron beam source is accomplished which generates an electron beam by impressing a negative voltage on the opposing electrode.