A spectrophotometer includes a xenon flash lamp, a spectroscope, and a light detector, wherein the spectrophotometer is configured to arrange a low-pressure mercury lamp on a bundle of light rays between the xenon flash lamp and the spectroscope on an as needed basis upon a performance determination of the spectrophotometer, and has a shutter mechanism that switches between shielding the bundle of light rays emitted from the low-pressure mercury lamp and allowing the bundle of light rays to pass through. A processing unit determines the performance of the spectrophotometer by detecting each of the light intensities with the light detector at the time when shielding the bundle of light rays and at the time when allowing the bundle of light rays by operating the shutter mechanism.