Abstract: Disclosed is a spectrophotometer capable of achieving a good signal-to-noise ratio by improving the use efficiency of the amount of light emitted from a Xe flash lamp or other intermittent light source. Light having a desired wavelength is selected from the light emitted from the Xe flash lamp (1), which is a single light source having a wide wavelength range, allowed to pass through a sample (7), detected by a photodetector (21, 22), and supplied to a low-pass filter (24) in a signal processing circuit (23). The duration of the waveform of a signal output from the photodetector (21, 22) is extended by the low-pass filter (24), which has a time constant equivalent to the elapsed time required for the intensity of the light emitted from the Xe flash lamp (1) to decrease from a peak value to a half value and acts as delay means or other duration extension means.