According to one embodiment, an optical disk device includes types of semiconductor laser diodes configured to emit laser light of different wavelengths, an output control circuit configured to control light output of each semiconductor laser diode, and a composite power source configured to generate voltages required for driving the types of semiconductor laser diodes and operating the output control circuit from a single power source voltage and to selectively output the generated voltages. The composite power source includes an input port to input an external control signal at a time of voltage selection and is configured to change the output voltage stepwise in response to the control signal.