Spectrophotometer

A spectrophotometer comprising:

• an infrared light source that emits exiting light including light having a wavelength within an infrared range;
• an interferometer that generates interference light based on the exiting light input thereto;
• a first detector that detects light generated based on the interference light that has been output from the interferometer, and has transmitted through or reflected from a sample;
• and
• a monitor unit that monitors an output of the infrared light source, wherein
• the monitor unit includes:
• a second detector that outputs a signal corresponding to an amount of the exiting light;
• and
• a light amount control unit that is operable to control the infrared light source such that the amount comes closer to a target light amount, based on the signal,
• the infrared light source emits light having a first wavelength range and light having a second wavelength range different from the first wavelength range, and
• the second detector includes:
• a first light detection element that outputs to the light amount control unit a first voltage corresponding to the light having the first wavelength range;
• and
• a second light detection element that outputs to the light amount control unit a second voltage corresponding to the light having the second wavelength range.