A hydraulic pump, comprising: a cylinder block having a plurality of cylinder bores and disposed so as to be rotatable; a plurality of pistons each retained in associated one of the plurality of cylinder bores so as to be movable; a swash plate for controlling an amount of movement of the plurality of pistons in accordance with a size of a tilt angle of the swash plate, wherein the tilt angle is an angle contained between a primary surface of the swash plate and a virtual plane perpendicular to an axis (Ax); a first pressing unit for pressing the swash plate in such a direction as to reduce the tilt angle of the swash plate; a second pressing unit for pressing the swash plate in such a direction as to increase the tilt angle of the swash plate by a pressure supplied from an outside of the hydraulic pump; and a first directional control valve including a spool, a spring for pressing the spool, and a fluid passage, wherein the pressure is a pressure corresponding to any of a negative flow control pressure (P N), a load-sensing flow control pressure (P LS), and a positive flow control pressure (P P), wherein a sensed back pressure of an orifice provided in a center bypass line running from the hydraulic pump via a control valve to a tank, at a portion between the control valve and the tank, constitutes the negative flow control pressure (P N), wherein the negative flow control pressure (P N) is input to the first directional control valve to control the position of the spool of the first directional control valve so as to switch the fluid passage in the first directional control valve and convert the negative control pressure (P N) to the pressure corresponding to the negative flow control pressure (P N), which is input to a pressure chamber of the second pressing unit, wherein the load-sensing flow control pressure (P LS) becomes smaller when the amount of fluid consumed in a hydraulic actuator becomes smaller than the amount of fluid discharged from the hydraulic pump, wherein the load-sensing flow control pressure (P LS) is converted to the pressure corresponding to the load-sensing flow control pressure (P LS), which is input to the pressure chamber of the second pressing unit, wherein a pilot pressure of a pilot operated valve for operating the valves is fed back to the hydraulic pump as the positive flow control pressure (P P), and wherein the pressure corresponding to the positive flow control pressure (P P) is directly input to the pressure chamber of the second pressing unit or is converted into another pressure corresponding to the positive flow control pressure (P P) before being input to the pressure chamber of the second pressing unit. a cylinder block having a plurality of cylinder bores and disposed so as to be rotatable; a plurality of pistons each retained in associated one of the plurality of cylinder bores so as to be movable; a swash plate for controlling an amount of movement of the plurality of pistons in accordance with a size of a tilt angle of the swash plate, wherein the tilt angle is an angle contained between a primary surface of the swash plate and a virtual plane perpendicular to an axis (Ax); a first pressing unit for pressing the swash plate in such a direction as to reduce the tilt angle of the swash plate; a second pressing unit for pressing the swash plate in such a direction as to increase the tilt angle of the swash plate by a pressure supplied from an outside of the hydraulic pump; and a first directional control valve including a spool, a spring for pressing the spool, and a fluid passage, wherein the pressure is a pressure corresponding to any of a negative flow control pressure (P N), a load-sensing flow control pressure (P LS), and a positive flow control pressure (P P), wherein a sensed back pressure of an orifice provided in a center bypass line running from the hydraulic pump via a control valve to a tank, at a portion between the control valve and the tank, constitutes the negative flow control pressure (P N), wherein the negative flow control pressure (P N) is input to the first directional control valve to control the position of the spool of the first directional control valve so as to switch the fluid passage in the first directional control valve and convert the negative control pressure (P N) to the pressure corresponding to the negative flow control pressure (P N), which is input to a pressure chamber of the second pressing unit, wherein the load-sensing flow control pressure (P LS) becomes smaller when the amount of fluid consumed in a hydraulic actuator becomes smaller than the amount of fluid discharged from the hydraulic pump, wherein the load-sensing flow control pressure (P LS) is converted to the pressure corresponding to the load-sensing flow control pressure (P LS), which is input to the pressure chamber of the second pressing unit, wherein a pilot pressure of a pilot operated valve for operating the valves is fed back to the hydraulic pump as the positive flow control pressure (P P), and wherein the pressure corresponding to the positive flow control pressure (P P) is directly input to the pressure chamber of the second pressing unit or is converted into another pressure corresponding to the positive flow control pressure (P P) before being input to the pressure chamber of the second pressing unit.