The Fourier transform infrared spectrophotometer includes: a light source 11 for generating infrared light having a wavelength width including an absorption wavelength of a compound to be analyzed; an interferometer including a fixed mirror 15 and a movable mirror 16, for generating interfering light from the infrared light; a detector 25 for generating a voltage with a magnitude corresponding to the intensity of the interfering light, and for outputting a voltage obtained by subtracting, from the aforementioned voltage, a voltage with a predetermined magnitude; a high-pass filter 464 for allowing the passage of frequency components equal to or higher than a predetermined frequency in an output voltage from the detector 25; an amplifier 463 for amplifying an output voltage from the high-pass filter 464 by a predetermined multiplying factor; and an analogue-to-digital converter 27 for converting an output voltage from the amplifier 463 into a digital signal.