A variable capacity piston pump performing suction and discharge of a hydraulic fluid by reciprocation of a piston in a cylinder block rotating integrally with a rotating shaft, the stroke of the reciprocation of the piston depending on an inclination of a swashplate, wherein the swashplate includes a sliding contact surface contacting slidably with one end portion of the piston via a shoe, the swashplate being disposed to enable to turn about a turning center to change the inclination that defines the stroke of the piston, the variable capacity piston pump comprising: a pressing portion disposed on one side with respect to the sliding contact surface of the swashplate, the pressing portion pressing a pressed portion (33,133) of the swashplate to adjust the inclination of the swashplate between a maximum inclination and a minimum inclination, wherein a discharge capacity of the hydraulic fluid is maximized at the maximum inclination and the discharge capacity of the hydraulic fluid is minimized at the minimum inclination, and a swashplate return spring disposed on the other side with respect to the sliding contact surface of the swashplate, the swashplate return spring extending along one direction and biasing the pressed portion of the swashplate toward the one side of the sliding contact surface, wherein the swashplate return spring is capable of taking a first seat surface center position and a second seat surface center position, wherein the first seat surface center position is a position of a seat surface center on the swashplate side when the inclination of the swashplate is the maximum inclination and the second seat surface center position is a position of the seat surface center on the swashplate side when the inclination of the swashplate is the minimum inclination, and and characterised in that there is a positional relationship in which a vertical reference line passes between the first seat surface center position and the second seat surface center position, the vertical reference line being a straight line perpendicular to a parallel reference line and passing through the turning center of the swashplate, the parallel reference line being a straight line parallel to an axial direction of the swashplate return spring and passing through the turning center of the swashplate. a pressing portion disposed on one side with respect to the sliding contact surface of the swashplate, the pressing portion pressing a pressed portion (33,133) of the swashplate to adjust the inclination of the swashplate between a maximum inclination and a minimum inclination, wherein a discharge capacity of the hydraulic fluid is maximized at the maximum inclination and the discharge capacity of the hydraulic fluid is minimized at the minimum inclination, and a swashplate return spring disposed on the other side with respect to the sliding contact surface of the swashplate, the swashplate return spring extending along one direction and biasing the pressed portion of the swashplate toward the one side of the sliding contact surface, wherein the swashplate return spring is capable of taking a first seat surface center position and a second seat surface center position, wherein the first seat surface center position is a position of a seat surface center on the swashplate side when the inclination of the swashplate is the maximum inclination and the second seat surface center position is a position of the seat surface center on the swashplate side when the inclination of the swashplate is the minimum inclination, and and characterised in that there is a positional relationship in which a vertical reference line passes between the first seat surface center position and the second seat surface center position, the vertical reference line being a straight line perpendicular to a parallel reference line and passing through the turning center of the swashplate, the parallel reference line being a straight line parallel to an axial direction of the swashplate return spring and passing through the turning center of the swashplate.