PURPOSE: To measure an energy loss spectrum simultaneously with simple constitution by arranging a quadrupole lens at an inlet and an outlet of a magnetic field sector type prism, and dispersing and converging the energy loss spectrum.

CONSTITUTION: An electron emitted from an electron source passes through a sample, and is made incident on a magnetic field sector type prism 6 through a quadrupole lens 5. The prism 6 has a magnetic field in the vertical direction to space, and as for an electron 15 whose energy loss is large, an orbit is bent in a small radius of curvature, and as for an electron 16 whose energy loss is small, an orbit is bent in a large radius of curvature, and the electron is dispersed by the energy loss. A quadrupole lens 7 regulates dispersion of a spectrum optionally, and projects it on a parallel detector 8. The lens 5 adjusts the focus on the detector 8. In this way, since the quadrupole lens is arranged at an inlet and an outlet of the sector type prism, an energy loss spectrum can be measured simultaneously with simple constitution.