An optical waveguide element module decreases discontinuity of electrical connection between an optical waveguide element and a relay substrate, without wire-bonding using long wires. An edge shape L of the signal electrode side of the ground electrode is surrounded by two shapes (L1, L2). Shape L1 is obtained by connecting an input end of the control electrode to a location where a space between the ground electrodes becomes W2. Shape L2 is such that an impedance change of the control electrode from the input end to the location at which the space between the ground electrodes becomes W2 is constant or continuously changes. A space between grounding wires connecting the ground electrodes of the element and ground lines of the relay substrate is larger than a space between the ground electrodes. In an embodiment, a terminal substrate and an output end of the control electrode are connected.