An orbiting fluid machine has a feature that the speed of sliding movement is low, while vibrations are small, its performance is lowered when the rotational speed becomes high, and this problem is resolved by the following structure. A displacement fluid machine includes a displacer making an orbital motion within a casing into which a working fluid is drawn, thereby drawing and discharging the working fluid, in which an oil retaining mechanism or a seal mechanism is provided at each of opposite end surfaces of the displacer. This results that, axial gaps at the end surfaces of the displacer are effectively sealed so as to reduce a leakage loss, thereby achieving a high performance and a high reliability.