An optical device includes an optical modulator formed on an optical IC chip. A shape of the IC chip is a rectangle or a parallelogram. The optical modulator includes an interferometer, wiring patterns, a first polymer pattern, and a second polymer pattern. The interferometer includes an optical waveguide that is formed in a direction from a first edge to a second edge of the optical IC chip. The wiring patterns are formed parallel to the optical waveguide. The first polymer pattern is formed along the first edge or the second edge. The second polymer pattern is connected to the first polymer pattern and formed on the optical waveguide without overlapping the wiring patterns.