Provided is an optical-waveguide-element module in which a common connecting substrate is used for different optical waveguide elements and deterioration of the propagation characteristics of electrical signals in a curved section of a signal electrode is suppressed. A control electrode in an optical waveguide element is consisted of a signal electrode SL and ground electrodes GD which put the signal electrode therebetween, a connecting substrate is provided with a signal line SL1 (SL2) and ground lines GD1 (GD2) which put the signal line therebetween, the signal electrode and the signal line, and, the ground electrodes and the ground lines are respectively connected to each other using wires (WR1, WR2, and WR20 to WR22) , the control electrode in which a space W1 between the ground electrodes GD at an input end or an output end of the control electrode is wider than a space W2 between the ground lines GD1 (GD2) on the optical waveguide element side in the connecting substrate, has a portion in which the space between the ground electrodes GD forms a space W3 which is narrower than the space W2 in a portion away from the input end or the output end, furthermore, the signal electrode SL in the control electrode has a curved section in a place from the input end or the output end to an operating part in which the control electrode applies an electric field to the optical waveguide, and suppression means (WR20 to WR32) for suppressing generation of a local potential difference between the ground electrodes which put the signal electrode therebetween in the curved section of the signal electrode is provided.