The device for the microbiological analysis of a support adapted to contain microorganisms marked by a fluorophore agent, said agent being adapted to absorb light energy with an absorption spectrum (53) having a crest (53') at a predetermined absorption wavelength (.lamda..sub.2) and to release that energy by emitting light with an emission spectrum (54) having a crest (54') at a predetermined emission wavelength (.lamda..sub.3) distinct from said absorption wavelength (.lamda..sub.2), comprises illuminating means; the spectrum (55) of the excitation light coming from the illuminating means having a crest (55') at a predetermined excitation wavelength (.lamda..sub.1) with a predetermined difference between the excitation (.lamda..sub.1) and absorption (.lamda..sub.2) wavelengths by virtue of which it is made easy to discriminate the light emitted by said fluorophore agent from that coming from the illuminating means.