There is provides a wavelength conversion apparatus for converting a wavelength of input signal light and for outputting output signal light of the converted wavelength. The apparatus includes a first and a second nonlinear mediums. The first nonlinear medium receives a first input light and outputs a first output light having a wavelength which is longer than that of the first input light, the wavelength being dependent on optical power of the first input light. The second nonlinear medium receives a second input light and a light output by a light source and outputs a second output light having a wavelength dependent on the wavelengths of the second input light and the light. The first output light is input as the second input light to the second nonlinear medium or the second output light is input as the first input light to the first nonlinear medium.