A method and apparatus for analyzing carbon isotope 14C is provided. A carbon isotope analyzer including an isotopic carbon dioxide generator to generate isotopic carbon dioxide from a carbon isotope; a spectrometer including an optical resonator having a pair of mirrors, and a photodetector to determine the intensity of light transmitted from the optical resonator; and a light generator including a light source, a first optical fiber to transmit a light beam from the light source, a second optical fiber for wavelength conversion, the second optical fiber branching from the first optical fiber at a point and combining with the first optical fiber at another point downstream of the branching point, and a non-linear optical crystal to generate light having the absorption wavelength of the isotopic carbon dioxide on the basis of the difference in frequency between light beams transmitted through the optical crystal.