To realize stable wavelength selecting action by sweeping wavelength at high speed by controlling laser wavelength without mechanically rotating a member having heavy mass.

The laser device has a laser resonator provided with a mirror having specified transmittance and adaptive optics, a laser medium disposed in the laser resonator and a dispersing element on which emitted light from the laser medium is made incident. Alternatively the laser device has a laser medium disposed in the laser resonator and capable of oscillating a laser in the wavelength region of a specified range, an adaptive optics having a mirror on which the emitted light from the laser medium is made incident, a grating on which the light reflected by the mirror of the adaptive optics is made incident and a mirror arranged so that the diffracted light from the grating may be reflected by the mirror of the adaptive optics and made incident, and having the specified transmittance.