A hybrid vehicle drive system including an engine, an electric motor operated by an electric energy stored in a storage device charged by operation of the engine, and a controller for selecting a low-load drive mode for driving the vehicle by the electric motor when the vehicle running condition is in a predetermined low-load range, and a high-load drive mode for driving the vehicle by the engine when the running condition is in a predetermined high-load range in which a load acting on the hybrid drive device is higher than that in the low-load range, and wherein the controller includes an emergency drive control device operated in the event of a failure of the first and second drive power sources, for operating the other, normal drive power source to drive the motor vehicle, and a range changing device for changing one of the low-load and high-load ranges which corresponds to the normal drive power source when the normal drive power source is operated by the emergency drive control device.