An optical device with an optical transmitter circuit and an optical receiver circuit integrated on a substrate has at least one of a first oblique waveguide extending obliquely with respect to an edge of the substrate at or near an incident port for introducing a light emitted from a light source to the optical device, a second oblique waveguide extending obliquely with respect to the edge of the substrate at or near a signal receiving port optically connected to the optical receiver circuit, and a third oblique waveguide extending obliquely with respect to the edge of the substrate at or near a signal transmission port optically connected to the optical transmitter circuit.