A cryogenic refrigerator includes a displacer and a cylinder therein for generating a very low temperature. And, a sealing ring is provided in an inserted condition within a ring shaped groove which is formed at an outer peripheral portion of the displacer, the sealing ring having resilience for extending itself outward so that a sealing member on an outer diameter thereof is enlarged and that an outer portion of the sealing ring is slidably contacted to an inner face of the cylinder, and the sealing ring being made of non-magnetic alloy, thereby a magnetic noise and disturbance of an outer magnetic field due to the cryogenic refrigerator are greatly decreased.