An optical device includes a first waveguide layer in which multiple-beam interference occurs, a second wavelength layer which includes a back surface facing the first waveguide layer and a front surface as a light output surface, and an outcoupling layer which is disposed on a back side of the second waveguide layer and faces the first wave guide layer, wherein the outcoupling layer includes a first portion as a layer with light transmission property and second portions which are dispersed in the first portion and differ in optical property from the first portion, and wherein an array of the second portions forms a triangular lattice.