An optical modulator 24 has a supporting substrate 5, a modulating substrate 11 made of an electro-optical material, an optical waveguide 12 provided on the side of a first main surface 30 of the modulating substrate 11, and an adhesion layer 6 adhering a second main surface 31 of the modulating substrate 11 onto the supporting substrate 5. The modulating substrate 11 has a high-frequency interaction portion 11c applying a voltage on the optical waveguide 12 to modulate propagating light, an incident portion 11a inputting light to the optical waveguide, and an outgoing portion 11b outputting light from the optical waveguide. The high-frequency interaction portion 11c is recessed on the first main surface 30 of the modulating substrate 11 with respect to the incident and outgoing portions 11a and 11b. The high-frequency interaction portion 11c has a thickness smaller than the those of the incident and outgoing portions 11a and 11b.