PURPOSE: To obtain a higher wavelength resolution of the Fourier transform spectroscope while its spatial resolution is being maintained.

CONSTITUTION: A Fourier transform spectroscope is provided with a light- splitting means BS which splits incident light from a measuring object into a reference light path and a measuring light path, with a fixed reflecting mirror M1 which is fixed and installed in the reference light path and which reflects light from the light-splitting means toward the light-splitting means, with a moving reflecting mirror M2 which is installed so as to be movable in the measuring light path and which reflects light from the light-splitting means toward the light-splitting means and with light-receiving means Lc, Dec by which light from the reference light path via the light-splitting means and light from the measuring light path via the light-splitting means are received. In the Fourier transform spectroscope, an afocal optical system 20 which is provided with magnifying magnification is arranged in a light path between the measuring object and the light-splitting means.