POWER SOURCE APPARATUS AND HYBRID CONSTRUCTION MACHINE EQUIPPED WITH SAME

Provided is a power source apparatus which suppresses wear of a electric storage device during continuous operation of a hydraulic pump under high-load pressure conditions and ensures assistance capability in subsequent normal work. The power source apparatus is equipped with a controller which carries out horsepower control to determine a flow rate of the hydraulic pump in accordance with a discharge pressure of the hydraulic pump detected by a pump pressure determination sensor. In horsepower control, the controller determines the flow rate in such a manner that a maximum input setting for the hydraulic pump which is defined by the discharge pressure and the flow rate is greater than the maximum output of the engine when the discharge pressure is discharge pressure Ppl, gradually becomes smaller as the discharge pressure changes from the discharge pressure Ppl towards a higher pressure, and becomes smaller than the maximum output of the engine when the discharge pressure is discharge pressure Pp3.