An optical device integrally including an optical waveguide and an optical detector, and a method of manufacturing the same. The optical device includes: a substrate; a first single crystalline growth layer grown on the substrate; an optical waveguide provided with a clad layer and a core layer formed on the first single crystalline growth layer; a second single crystalline growth layer grown on a predetermined portion of a core layer at which the clad layer is removed, for absorbing light having a wavelength within a predetermined band and traveling in the optical waveguide.