PURPOSE: To provide a tunable laser device which can make a spectral width for wavelength selection use remarkably narrow.

CONSTITUTION: In conventional devices, an optical element for wavelength selection use is installed at the inside of a resonator. Since a spectral width amounts to only about 0.1nm, the range of an applicable spectroscopic optical element is limited. As a wavelength selection element, crystallized quartz or calcite can be used in addition to a birefringent filter, but the spectral width can be made narrow down to only about 0.1nm. At this invention, a laser oscillator is equipped with a feedback means. Thereby, one part of a laser beam is taken out to the outside of a resonator; it is passed through an optical element for wavelength selection use such as a grating or the like and, after that, is returned to the resonator. As a result, the laser beam whose spectral width has been made narrow by using the optical element is amplified by using a laser medium.