PURPOSE: To efficiently convert a rotational speed by transmitting a fluid pressure, generated between a cylinder and a piston which is reciprocated by a swash plate driven by a first and second rotary shafts, through fluid passages of a valve block between both the rotary shafts.

CONSTITUTION: Cylinder barrels CB3, 4 are connected to a first and second rotary shafts 1, 2, and a valve block 5 is provided between the cylinder barrels. A plurality of cylinders 6 and pistons 7 are provided in the circumferential direction of the cylinder barrel CB3, and protrusive parts of the pistons 7 are contacted to a swash plate 10 driven by the shaft 1, by a pad 8 to perform a swinging motion and a reciprocating motion in the direction of the shaft 1. While protrusive parts of pistons 14 of a plurality of cylinders 13 in the circumferential direction of the cylinder barrel CB4 are contacted to a swash plate 17 of the shaft 2 to perform a swinging motion and a reciprocating motion in the direction of the shaft 2. A fluid pressure, generated in the cylinders 6, 13, is transmitted through common fluid passages 26, 27 by switching selector valves 22, 23 with drive rods 24, 25 in the valve block 5. In this way, a rotational speed is efficiently converted.