Spectrophotometer intended in particular for the optical analysis of samples in a rotatory analyser. In order to attain the characteristics required of a modern spectrophotometer for clinical chemistry and to attain in particular a high reproducibility of the measurements, the spectrophotometer comprises a flash tube, an stabilizing optical device for device for deriving a light beam having a constant spatial distribution from each flash from the flash tube, a grating monochromator for dispersing the light delivered by the stabilizing device and for delivering a beam of filtered light, an optical element for dividing the filtered beam to produce two beams, the first of which travels through a sample for analysis and the second of which reaches a detector which delivers a reference signal corresponding to the intensity of the second beam, and a second detector placed to receive the beam emerging from the sample.