The object of the present invention is to carry out control and enable an engine to output a desired power, thereby preventing unexpected charge or discharge of storage battery means. A power output apparatus of the present invention sets energy Pe to be output from an engine, in order to cancel a deviation .DELTA.Pb of a charge-discharge electric power Pb of a battery from its target value Pb* , and controls operation of the engine to output the energy Pe. The energy Pe output from the engine is subjected to torque conversion by means of a clutch motor and an assist motor and output to a drive shaft as a required power. In case that the converted energy is not equal to the required power, the battery is charged with the surplus electric power or is discharged to supplement the shortage of electric power. Namely regulation of the energy Pe results in controlling the charge-discharge electric power Pb of the battery. When the target value Pb* is set equal to zero, the power output apparatus enables a desired power to be output to the drive shaft without causing unexpected charge or discharge of the battery.