the invention can prevent gas leakage and reduce friction force while relaxing tolerance for manufacturing a displacer and the like for stirling cycle machines . gas leakage between the outer periphery of a seal and the inner peripheral surface of a cylinder is prevented . accordingly , precise finish of the radial clearance between the displacer and the cylinder is not required . as the difference of pressures between the front and rear spaces of the displacer is small , the gas leakage is sufficiently prevented without pressing the seal against the inner peripheral surface of the cylinder . on the other hand , as the friction force generated between them is significantly small , it does not affect the reciprocation of the displacer . as the seal is provided so as not to be restricted axially and radially , the displacer is kept closely contacted with the inner peripheral surface of the cylinder even if the displacer eccentrically shifts .