The optical device includes a substrate having an electrooptic effect; a plurality of optical waveguides formed in the substrate in parallel to one another; and a polarization inversion region which is disposed a part of the substrate and which has a polarization characteristic that is an inverse to that of the substrate, wherein a profile of a boundary between the polarization inversion region and a remaining region in which the polarization is not inverted is configured such that accumulated amounts of distortion that affects the respective waveguides over coordinates along a light propagation direction are substantially identical.