A detecting device for a spectrophotometer is provided which is capable of exhibiting a sufficient sensitivity and with an adequate linearity over the ultraviolet light, visible light and near-infrared light ranges. The spectrophotometer detecting device includes detectors of a photomultiplier-tube detector, an InGaAs detector and a PbS detector, and a switching device for switching among these detectors. Alternatively, the spectrophotometer may include a single integrating sphere including these three types of detectors placed thereon. The spectrophotometer may further include output conversion means for correcting the output linearity difference among these detectors.