Abstract: An improvement of biasing means which urges a piston shoe guide member of an axial piston type hydraulic pump/motor toward a swash plate is provided. Biasing means comprises a plug which is partly inserted into a cylinder bore of a reduced diameter formed in a cylindrical block which receives a plurality of axial pistons, a compressing spring received within the cylinder bore for urging the plug toward the piston shoe guide member, and check valve means which closes the cylinder bore to exert an increased force of reaction upon the piston shoe guide member as the piston shoe guide member drives the plug inwardly and which provides a communication between the cylinder bore and the outside of the cylinder block as the piston shoe guide member tends to move away from the plug.