In an optical waveguide supplied with electricity by using a heater, miniaturization of the device is achieved by enhancing heat dissipation efficiency and heat resistance. In a modulator including an optical waveguide formed on an insulating film, a first interlayer insulating film that covers the optical waveguide, a heater formed on the first interlayer insulating film, and a second interlayer insulating film that covers the heater, a heat conducting portion adjacent to the optical waveguide and the heater and penetrating the first and second interlayer insulating films is formed.