Provided is a Fourier transform-type spectroscopic device capable of improving an acquisition speed of a molecular vibration spectrum. The Fourier transform-type spectroscopic device (1) of the present invention rotates a scanning mirror (26b) by rotation of a rotating shaft (26a) to change a light path length of scanning light and delay or advance the scanning light with respect to reference light in accordance with a rotation angle of the scanning mirror (26b) from an initial position, and is thus capable of moving the scanning mirror (26b) at a high speed as compared with a case where a movable mirror is mechanically moved as in a conventional Fourier transform-type spectroscopic device, thereby improving an acquisition speed of a molecular vibration spectrum.