PURPOSE: To selectively use a detector with the necessary response speed by providing multiple detectors with different response speeds in advance and changing the deflection direction of secondary electrons.

CONSTITUTION: An electromagnetic coil 30 generating the magnetic field and deflecting plates 31 and 32 generating the electric field are mounted on an objective lens 6 to constitute a deflector. The secondary electrons 3 emitted from a sample are converged by a lens section 6 and diverged and deflected by the deflector. Only those of the deflected secondary electrons surmounting the reverse electric field of a control grid 5 are detected by a secondary electron detector. The first high-speed detector 4 has the high-speed responsiveness of 5W10ns, when the polarities of the electrostatic deflecting plates 31 and 32 and the electromagnetic coil 30 are reversed, the secondary electrons are deflected in the reverse direction 3' and detected by the second low-speed detector 4' with the responsiveness of 20ns. The high-speed response detector and the low-speed response detector can be selectively used only by changing the polarity of the deflector.