A sealing device configured to seal an annular gap between a shaft and a housing that move relative to each other, the sealing device comprising: a seal ring made of resin; and an elastic seal ring made of a rubber-like elastic body, the elastic seal ring being attached to an outer circumference surface side of the resin seal ring and configured to be in close contact with an inner circumference surface of a shaft hole through which the shaft is inserted in the housing, wherein the resin seal ring includes: a cylindrical section; a pair of inner circumference lips respectively provided on both sides of the cylindrical section in an axial direction; a pair of outer circumference lips respectively provided on both sides of the cylindrical section in the axial direction; and an annular mounting groove which is provided on an outer circumference surface of the cylindrical section and in which the elastic seal ring is mounted, each of the pair of inner circumference lips is reduced in diameter with distance from the cylindrical section both on an inner circumference surface side and an outer circumference surface side toward lip distal ends, which are configured to slide on an outer circumference surface of the shaft, and each of the pair of outer circumference lips is increased in diameter with distance from the cylindrical section both on an inner circumference surface side and an outer circumference surface side toward lip distal ends, which are configured to be in close contact with the inner circumference surface of the shaft hole, and the sealing device has only the one elastic seal ring which is provided only on the outer circumference surface side of the resin seal ring, and the elastic seal ring is in close contact with the groove bottom surface of the mounting groove in the resin seal ring because the inner diameter of the elastic seal ring is smaller than the outer diameter of the groove bottom surface of the mounting groove in the resin seal ring, characterised in that in the state in which an external force does not act, the outer diameter of the elastic seal ring is smaller than the outer diameter of the lip distal ends of the pair of outer circumference lips in the resin seal ring. a seal ring made of resin; and an elastic seal ring made of a rubber-like elastic body, the elastic seal ring being attached to an outer circumference surface side of the resin seal ring and configured to be in close contact with an inner circumference surface of a shaft hole through which the shaft is inserted in the housing, wherein the resin seal ring includes: a cylindrical section; a pair of inner circumference lips respectively provided on both sides of the cylindrical section in an axial direction; a pair of outer circumference lips respectively provided on both sides of the cylindrical section in the axial direction; and an annular mounting groove which is provided on an outer circumference surface of the cylindrical section and in which the elastic seal ring is mounted, a cylindrical section; a pair of inner circumference lips respectively provided on both sides of the cylindrical section in an axial direction; a pair of outer circumference lips respectively provided on both sides of the cylindrical section in the axial direction; and an annular mounting groove which is provided on an outer circumference surface of the cylindrical section and in which the elastic seal ring is mounted, each of the pair of inner circumference lips is reduced in diameter with distance from the cylindrical section both on an inner circumference surface side and an outer circumference surface side toward lip distal ends, which are configured to slide on an outer circumference surface of the shaft, and each of the pair of outer circumference lips is increased in diameter with distance from the cylindrical section both on an inner circumference surface side and an outer circumference surface side toward lip distal ends, which are configured to be in close contact with the inner circumference surface of the shaft hole, and the sealing device has only the one elastic seal ring which is provided only on the outer circumference surface side of the resin seal ring, and the elastic seal ring is in close contact with the groove bottom surface of the mounting groove in the resin seal ring because the inner diameter of the elastic seal ring is smaller than the outer diameter of the groove bottom surface of the mounting groove in the resin seal ring, characterised in that in the state in which an external force does not act, the outer diameter of the elastic seal ring is smaller than the outer diameter of the lip distal ends of the pair of outer circumference lips in the resin seal ring.