Using a scanning electron microscope equipped with a low-temperature stage, we show that under the electron irradiation a superconducting tunnel junction can operate regularly. The electron beam generates a voltage signal across the current-biased junction. By recording the small voltage change synchronously with the coordinate irradiated by the beam, a two-dimensional "voltage image" of the density distribution of the junction tunneling current can be obtained. The distributions are in agreement with the magnetic interference patterns of the dc-Josephson currents in the junctions. © 1982.