A power output apparatus that suppresses wearing-out of the components of a transmission connected to a drive shaft and a rotating shaft of an electric motor as well as reducing the a shock imparted to the vehicle. The required drive power is output to the drive shaft by appropriately controlling and internal combustion engine, a power split device, the electric motor and a shifting portion. When the rotational speed of the drive shaft can be estimated, the speed ratio in the shifting portion is changed based on either the detected rotational speed of the drive shaft or the estimated rotational speed of the drive shaft and the rotational speed of the rotating shaft. However, when the rotational speed of the drive shaft cannot be estimated, the speed ratio is maintained in the shifting portion.