Abstract: A control method of a system for generating hydraulic power, the system including an internal combustion engine controlled by fuel injection from a fuel injection pump, and a plurality of hydraulic pumps of the variable displacement type. An engine speed deviation is obtained by calculating a difference between a target engine speed set by a manipulated variable of an accelerator for the internal combustion engine and an output engine speed of the engine. The engine speed deviation is converted into a pump control coefficient which is in a functional relation with this deviation. A calculation is performed with the converted value and an externally manipulated variable for inclination of a swash plate of the hydraulic pump, and the calculated value is supplied to a regulator of the hydraulic pump as a target value for inclination of the swash plate thereof to thereby control the inclination angle of the swash plate of the hydraulic pump.