PURPOSE: To provide a spectroscope for obtaining high resolution and wide wavelength range solely by providing optical path switching means and selecting number of transmissions of the spectroscope.

CONSTITUTION: A two-stage type spectroscope has a slit 2 for introducing an emitting light of a light source 1, and a slit 6 for emitting a light having a specific wavelength of the incident emitting lights of the source 1, wherein the emitted light from the source 1 is transmitted twice to the spectroscope, and comprises optical means 11 which is incident a second stage output light of the spectroscope and reflects it to cross it with first-stage output light, optical path switching means 14 disposed at an intersection of the second-stage output light reflected by the means 11 and the first-stage output light to switch a state in which the first-stage output light is reflected in the same direction as that of the two-stage output light and a state in which the first-stage output light is not reflected and passed in a direction of the two-stage input.