A wavelength tunable light source equipment provided with an external resonator light source having a wavelength selection structure inside it and lasing by a wavelength selected by this and a light path changer introducing at least part of the light emitted from the external resonator light source and including a spontaneous emitted light ingredient to the wavelength selection structure so that a wavelength of the light emitted from the external resonator light source and a wavelength selected by the wavelength selection structure become synchronized. Of the light emitted from the external resonator light source, the light introduced to the wavelength selection structure through the light path changer and emitted from it is made the output light. Due to this configuration, it is possible to reduce the resonator loss of the external resonator light source to stabilize the oscillation in the laser resonator, increase the intensity of the output light with the suppressed spontaneous emitted light ingredient, and finely adjust and freely change the relationship between the intensity of the output light including the spontaneous emitted light ingredient and the intensity of the output light with the suppressed spontaneous emitted light ingredient.