To provide an inclined shaft type variable displacement pump motor positively detecting position of a tilt angle control piston with simple constitution without requiring a new stroke length for detecting the position of the tilt angle control piston.

A sliding surface 20a of the tilt angle control piston 20 is formed with a conduction groove 23 for leading pilot pressure into a pilot pressure lead-in hole 28 from a pilot pressure lead-in port 27 formed in a cylinder casing 2b. A guide valve 22 is controlled by the pilot pressure led into the pilot pressure lead-in hole 28 and by a spring 24 disposed in an oil chamber 30. An inclined face 19 extending along the sliding direction of the tilt angle control piston 20 is formed using a part of the conduction groove 23. The sliding quantity of a probe 15 brought into contact with the inclined face 19 is detected by a displacement detector 17 to detect the stroke position of the tilt angle control piston 20.