In a semiconductor chip module, a transmission optical waveguide device to be mounted in the proximity of the side face of a semiconductor chip on a circuit board includes an input optical waveguide to which light from an external light source is inputted, an output optical waveguide provided at a position displaced in a vertical direction to the surface of the circuit board in a mounted state on the circuit with respect to the input optical waveguide for outputting an optical signal to a different device, an optical path changeover structure for guiding light guided through the input optical waveguide to the output optical waveguide, and an optical modulator provided on the input optical waveguide or the output optical waveguide for modulating light from the external light source based on an electric signal from the semiconductor chip.