Abstract: A swash-plate plunger-type hydraulic device has a cylinder block with a plurality of plungers slidably fitted in cylinder bores, a swash plate confronting one end of the cylinder block, and a distribution valve plate slidably held against the other end of the cylinder block. The cylinder block has an even number of circularly arrayed connecting ports communicating with the cylinder bores and opening at the other end thereof. The distribution valve plate has inlet and outlet ports. The cylinder block is rotatable through an angular displacement .theta.1 in which the hydraulic pressure in one connecting port between the inlet and outlet ports increases from a lower pressure to a higher pressure, through an angular displacement .theta.2 in which the hydraulic pressure in one connecting port between the inlet and output ports decreases from the higher pressure to the lower pressure, and through an angular displacement .theta.