A first film (8) is formed between a substrate (1) constituting an optical waveguide device (10) and a signal electrode (3) and ground electrodes (5), (6). A second film (9) is formed between the substrate (1) and a signal electrode (4) and ground electrodes (6), (7). The substrate (1), an optical waveguide (2), the signal electrode (3), the ground electrodes (5), (6) and the first film (8) constitute an optical phase modulator (10A). The substrate (1), the optical waveguide (2), the signal electrode (4), the ground electrodes (6), (7) and the second film (9) constitute an optical intensity modulator (10B). The optical waveguide element (10) is constituted by integrating the optical phase modulator(10A) and the optical intensity modulator (10B).