<p>Provided is an optical waveguide element module wherein a filter circuit including a capacitor is disposed on a line for inputting a modulation signal into a modulation electrode of an optical waveguide element. The optical waveguide element module can smooth an optical response frequency characteristic over a wide band of several dozen GHz even if a multilayer ceramic capacitor is used as the capacitor. The optical waveguide element module includes an optical waveguide element having a substrate (1) formed of a material having an electro-optic effect, an optical waveguide (2) formed on the substrate, and a modulation electrode (3) for modulating optical waves propagated over the optical waveguide, and a filter circuit (7) which is disposed on a line for inputting a modulation signal into the modulation electrode and includes a capacitor. As for the capacitor, only a multilayer ceramic capacitor having a capacitance per each of 3 pF or below is used.</p>
