A power plant which is capable of improving the drive efficiency and the power generation efficiency thereof when the electric power is generated using the power of a driven part thereof. A power plant has an internal combustion engine having a crankshaft, and a rotary motor having a rotor. A planetary gear train includes a sun gear, a ring gear, and a carrier rotatably supporting a planetary gear in mesh with the sun gear and the ring gear. The sun gear and the ring gear are connected to drive wheels. The carrier is connected to the crankshaft. The rotor is connected between one of the sun gear and the ring gear and the drive wheels. A transmission is connected between the other of the gears and the drive wheels, for varying a speed of power of the engine and transmitting the power to the drive wheels.