A driving gear of a vehicle comprising a motor generator (MG2), a power control unit (21) for controlling the motor generator (MG2), and a case for containing the motor generator (MG2) and the power control unit (21). The power control unit (21) comprises a first inverter for driving the motor generator (MG2), and a voltage converter for applying power supply voltage to the first inverter after stepping it up. The voltage converter includes a reactor (L1). Heat of the reactor (L1) is dissipated using lubricant touching the reactor (L1) and the case as heat transfer agent. A circulation path of lubricant is formed in the case and the reactor is arranged on the circulation path.