To provide a wavelength conversion element capable of easily converting the wavelength of an inputted signal light with the same efficiency regardless of the polarization state of the signal light.

This element is provided with an active region 2 having a bulk structure which is provided on a substrate 1 and to which a tensile strain is applied in the direction vertical to the propagation direction of a light and parallel with a lamination direction and in which a gain with respect to a light which has an electric field in the direction vertical to the propagation direction and parallel with the lamination direction is increased so as to become equal to a gain with respect to a light which has an electric field in the direction vertical to the propagation direction and vertical to the lamination direction and a diffraction grating 3 which is adjacent to the active region 2 and has the periodic variation of refractive index in the propagation direction of the light.