To reduce loss of pump hydraulic power, and form a device in a compact size by arranging swash plate control structures composed of a control piston for push-pressing a swash plate in a swash plate type twin pump in the slantly rotating direction and a plurality of return springs for controlling horse power in a direction against push-press force, at two positions.

In a twin swash plate type piston pump wherein pistons 18 are fitted to a plurality of cylinders 17 drilled on cylinder blocks 13, 14, tips of two control pistons 25, 25 which are slidably fitted to a housing 10 and which are disposed in parallel with each other, are brought into push-contact with one side extending part 24 of a swash plate 20. Two return springs 28, 28 which are disposed in parallel with each other are arranged on the other side extending part 27. Each return spring 28 energizes the other side of the swash plate 20 by total four springs as two pieces matching springs 30, 31. The total length of four springs is designed short step by step in four steps, and thereby, spring reaction is acted in order.