Herein disclosed is an optical modulation device, comprising: a substrate 1 having a polarization non-reversal region 17a and a polarization reversal region 17b; an optical waveguide 18 including first and second branched optical waveguide portions 18a, 18b; and a traveling waveguide including a center electrode 19a and a ground electrode 19b, 19c to have an electric signal applied thereto, said traveling waveguide and said first and second branched optical waveguide portions collectively forming an interaction portion to have said incident light interacted with said electric signal, said interaction portion being constituted by a first interaction sub-portion 20a and a second interaction sub-portion 20b, said first and second interaction sub-portions being respectively positioned in regions of said substrate having opposite polarization orientations with each other, in which said center electrode is positioned in face to face relationship with one of said first and second branched optical waveguide portions at said first and second interaction sub-portion to ensure that said incident light in said first and second branched optical waveguide portions are phase modulated, and in which said interaction portion includes an optical waveguide shift sub-portion sandwiched between said first and second interaction sub-portions to have positions of said first and second branched optical waveguide portions shifted therein in a transverse direction, ensuring that positions of said first and second optical waveguides relative to said center and ground electrodes are interchanged between said first and second interaction sub-portions.