To provide a swash plate type hydraulic pump motor for largely securing the practical volume ratio still in a small type.

This swash plate type hydraulic pump motor has first and second swash plates 30 and 40 for oppositely reciprocating first and second pistons 8 and 9 so as to expand and contract a volume chamber 10 in response to rotation of a cylinder block 4, first and second swash plate bearings 32 and 42 for tiltably supporting the first and second swash plates 30 and 40, a valve element 60 rotatably inserted into the cylinder block 4, a pair of supply discharge ports 61 opening in an outer peripheral surface of this valve element 60, and a cylinder port 11 opening in an inner peripheral surface of the cylinder block 4, and intermittently communicating with these supply discharge ports 61.