A driving device of the invention is mounted on a motor vehicle, where a sun gear, a carrier, and a ring gear of a planetary gear mechanism are respectively connected to a motor MG1, to an engine, and to a drive shaft and a motor MG2. The driving device has a power supply system including a capacitor, a transistor TR, and a diode DI. The capacitor is connected to power lines, which are shared by inverters for the motors MG1 and MG2 and are linked to a battery via a DC-DC converter. The transistor TR is located between the power lines and the capacitor and is arranged in a direction of charging the capacitor. The diode DI is arranged in an opposite direction in parallel with the transistor TR. Drive control of the transistor TR and the DC-DC converter converts an output voltage of the battery into a desired voltage level and outputs the converted voltage to the power lines, while adequately controlling charge and discharge of the capacitor. Adequate charge and discharge of the capacitor enables output of a preset power demand to the drive shaft and ensures the improved driving performance.