A screw pump includes a pump housing in which a pump spindle is rotatably mounted with the involvement of a hydrostatic thrust bearing for absorbing the axial thrust which is produced at the spindle during operation, the hydrostatic thrust bearing being formed by a housing-fixed bearing surface, against which an end-face, spindle-fixed bearing surface of the pump spindle is indirectly supported, by virtue of the fact that the housing-fixed bearing surface and the spindle-fixed bearing surface form a bearing gap therebetween, which bearing gap is fed, in its central region, with a pressure fluid which flows out through the bearing gap in the radial direction, preferably into the intake region, and the hydrostatic pressure of which counteracts the axial thrust.

In a rotary compressor, when it is assumed that a vane width is W, the amount of eccentricity of an eccentric portion is e, a vane leading end curvature radius is R.sub.v, an annular piston radius is R.sub.ro, and a non-sliding region width on each of both side portions of a vane leading end is W.sub.t, the vane width W and the vane leading end curvature radius R.sub.v are set such that the non-sliding region width W.sub.t on each of both the side portions of the vane leading end defined by the following equation (A) is a value satisfying an equation (B):

W.sub.t=(W/2)eR.sub.v/(R.sub.v+R.sub.ro)(A)

0.3 mmW.sub.t0.6 mm(B).