An object of the present invention is to provide an optical waveguide element module where the bonding wires can be prevented from disengaging or disconnecting so as to provide high reliability. Another object is to provide an optical waveguide element module that can be made compact and where an increase in the manufacturing cost can be minimized. An optical waveguide element module having: a waveguide substrate 1 on which an optical waveguide (not shown) and control electrodes (E1 to E4) for controlling light waves that propagate through the optical waveguide are formed; external substrates (21 to 24) having wire circuits (TM1, C1), which are connected to control electrodes electrically, disposed proximity to the waveguide substrate; a housing 3 in which the external substrate and the waveguide substrate are arranged; and terminals (T21 to T24) which are connected to an external electric circuit (not shown) for supplying electrical signals to the control electrode or deriving electrical signals from the control electrode provided with the housing, wherein relay electrode pads (CP1, CP4) which are electrically isolated from both of the wiring circuit and the control electrode are formed in any portion of the waveguide substrate 1 and the external substrates (21 to 24), and at least one bonding wire (W21, W22, W41, W42) is connected from a control electrode to the terminal or from the wire circuit to the terminal via the relay electrode pad.