Tandem piston pump from which 4-line pump discharge pressures are outputted, including front swash plate (14) and rear swash plate (54) with respective tilt rotation axis directions different from each other, structured so that individual discharge ports (23,24) of rear pump (50) open with a phase difference from individual discharg ports (21,22) of front pump (10) and so that individual pump ports (41,42) of the front pump (10) and individual pump ports (43,44) of the rear pump (50) open on different side faces (71,72) of port block (70).