Patent ID: 8000359

Claim:
An external resonator type laser device provided with a resonator including a wavelength selective filter and a semiconductor light amplifier having a phase adjustment region for changing a phase of light passing through the wavelength selective filter in accordance with a phase adjustment signal from outside and a light amplifying region, wherein a wavelength margin between a peak transmission wavelength at which a transmittance of the wavelength selective filter becomes the maximum and a mode hop occurring wavelength on a short wave side is smaller than that on a long wave side, the laser device comprising: light intensity detecting means for detecting light intensity of light emitted from the resonator; phase adjustment signal varying means for varying the phase adjustment signal to be applied to the phase adjustment region so that the light intensity detected by the light intensity detecting means becomes the maximum; and phase adjustment signal oscillating means for oscillating the phase adjustment signal to be applied to the phase adjustment region with a period shorter than a period of variation by the phase adjustment signal varying means, wherein the light intensity detecting means detects the light intensity only during a period in which a wavelength of the light emitted from the resonator is deviated to the short wave side in accordance with the oscillation of the phase adjustment signal by the phase adjustment signal oscillating means.