A light-emitting body of rapid speed of response and high light emission intensity, and an electron beam detector, scanning electron microscope and mass spectroscope using this are provided. In the light-emitting body 10 according to the present invention, when fluorescence is emitted by a nitride semiconductor layer 14 formed on one face 12a of a substrate 12 in response to incidence of electrons, at least some of this fluorescence is transmitted through this substrate 12, whereby that fluorescence is emitted from the other face 12b of the substrate. The response speed of this fluorescence is not more than μsec order. Also, the intensity of emission of this fluorescence is almost identical to that of a conventional P47 phosphor. Specifically, with this light-emitting body 10, a response speed and light emission intensity are obtained that are fully satisfactory for application to a scanning electron microscope or mass spectroscope. In addition, a cap layer 16 contributes to improvement in the persistence rate of light emission in the nitride semiconductor layer 14, so, with this light-emitting body 10, not only high-speed response and high light emission intensity are obtained, but also an excellent persistence rate.