A first film (8) is formed between a substrate (1) and a signal electrode (3); ground electrodes (5) and (6) which constitute an optical waveguide device (10), and a second film (9) is formed between the substrate (1) and a signal electrode (4); ground electrodes (6) and (7). An optical phase modulator (10A) is composed of the substrate (1), an optical waveguide (2), the signal electrode (3), the ground electrodes (5) and (6), and the first film (8). An optical intensity modulator (10B) is composed of the substrate (1), the optical waveguide (2), the signal electrode (4), the ground electrodes (6) and (7), and the second film (9). The optical waveguide device (10) is composed of the optical phase modulator (10A) and the optical intensity modulator (10B), which are integrated monolithically.