It is an object of the present invention to provide a variable wavelength light source apparatus capable of changing continuously wavelengths of a plurality of oscillation light over a wideband and an optical amplifier using the same. In order to achieve the above object, the variable wavelength light source apparatus comprises: a wavelength selection device in which a propagation direction of emitted light is changed according to a wavelength of incident light; a plurality of light sources emitting the light that has reciprocated in a gain medium with a high reflecting mirror on an end face thereof and has been amplified, to a predetermined position of the wavelength selection device at angles different from each other; an optical resonance reflection section reflecting a part of the light incident vertically out of the emitted light from the wavelength selection device to form an optical resonator configuration between the optical resonance reflection section and each of the high reflecting mirrors of the light sources to generate oscillation light; an optical coupler section coupling the oscillation light transmitted through the optical resonance reflection section in an output light path; and a drive section changing an arrangement angle of the wavelength selection device with respect to the optical resonance reflection section according to desired wavelength setting.