A high-frequency superposing module for driving a laser diode includes an oscillating circuit and an impedance matching circuit. The impedance matching circuit includes a capacitor connected in series between the emitter of a transistor and the terminal through which a laser-diode drive signal is output; and a capacitor connected in parallel between the drive-signal output terminal and the ground. The oscillating circuit includes an inductor serving as a choke coil connected between the drive-signal output terminal and the collector of the transistor, thus allowing the drive-signal output terminal to serve as a power input terminal for the oscillating circuit.