An electron source producing an electron beam which is highly reliable and stable even when it is externally oscillated. The support table includes a plurality of support protrusions that contact the substrate during use for supporting the substrate. As a result, when the device is illuminated by a common illumination beam of multi-wavelength illumination, spectral analysis performed on the reflected or transmitted illumination enables simultaneous sensing of a plurality of substances or environmental conditions. Means are provided to cause the plate to move to the slanted position in response to the closing of a paper tray of a printer or copier.