An optical modulation apparatus includes: a substrate; a first optical waveguide and a second optical waveguide formed at an interval on the substrate; an electrode provided along at least one of the first optical waveguide and the second optical waveguide; and a power source coupled to the electrode to apply a voltage to at least one of the first optical waveguide and the second optical waveguide, wherein at least one of the first optical waveguide and the second optical waveguide includes a diffraction grating region where light having a wavelength λ is reflected, and a phase shift region where a phase of the light is shifted by an amount in a range of 0 to λ/2.