PURPOSE: To detect secondary electrons with high efficiency by converging light which is converted from the secondary electrons by using a fluorescent optical fiber.

CONSTITUTION: An electron beam 1 emitted by an electron gun irradiates a sample 3 after converged thinnly by an objective 2 and a secondary electron 4 from the sample 3 is detected by a secondary electron detector 5 to become a video signal. The detector 5 consists of a scintillator 51, the fluorescent optical fiber 52, and a photomultiplier and when the secondary electron 4 is converted by the scintillator 51 into light, the light is made incident on the flank of the fluorescent optical fiber 52 and its fluorescent agent contained in the fiber fluoresces, so its light can be guided axially out of the optical fiber 52. For the purpose, the detector 5 is constituted symmetrically about the axis and the light emitted by the scintillator 51 is detected sufficiently to obtain high resolution and high detection efficiency.