A sealing device for sealing an annular gap between a shaft and a housing comprising: a packing made of resin having an outer circumferential lip on an outer circumferential side with respect to an annular mounting groove provided on a sealed fluid side, when the sealing device is in use, and an inner circumferential lip on an inner circumferential side with respect to the annular mounting groove; and a metal spring member mounted in the mounting groove and having an outer circumferential pressing portion extending radially outward and toward the sealed fluid side, when the sealing device is in use, from a groove bottom of the mounting groove and pressing the outer circumferential lip radially outward, and an inner circumferential pressing portion extending radially inward and toward the sealed fluid side, when the sealing device is in use, from the groove bottom of the mounting groove and pressing the inner circumferential lip radially inward, wherein a thickness of the outer circumferential lip in a thinnest portion thereof on a proximal end side from a portion thereof with a largest outer diameter is smaller than a thickness of the inner circumferential lip in a thinnest portion thereof on a proximal end side from a portion thereof with a smallest inner diameter, wherein, among the outer circumferential lip and the inner circumferential lip, a protrusion that prevents the spring member from coming off is provided only on the inner circumferential lip, and the outer circumferential lip extends toward the sealed fluid side and beyond a distal end of the outer circumferential pressing portion of the spring member mounted in the mounting groove, characterized in that a length of the outer circumferential lip in an axial direction is shorter than the inner circumferential lip. a packing made of resin having an outer circumferential lip on an outer circumferential side with respect to an annular mounting groove provided on a sealed fluid side, when the sealing device is in use, and an inner circumferential lip on an inner circumferential side with respect to the annular mounting groove; and a metal spring member mounted in the mounting groove and having an outer circumferential pressing portion extending radially outward and toward the sealed fluid side, when the sealing device is in use, from a groove bottom of the mounting groove and pressing the outer circumferential lip radially outward, and an inner circumferential pressing portion extending radially inward and toward the sealed fluid side, when the sealing device is in use, from the groove bottom of the mounting groove and pressing the inner circumferential lip radially inward, wherein a thickness of the outer circumferential lip in a thinnest portion thereof on a proximal end side from a portion thereof with a largest outer diameter is smaller than a thickness of the inner circumferential lip in a thinnest portion thereof on a proximal end side from a portion thereof with a smallest inner diameter, wherein, among the outer circumferential lip and the inner circumferential lip, a protrusion that prevents the spring member from coming off is provided only on the inner circumferential lip, and the outer circumferential lip extends toward the sealed fluid side and beyond a distal end of the outer circumferential pressing portion of the spring member mounted in the mounting groove, characterized in that a length of the outer circumferential lip in an axial direction is shorter than the inner circumferential lip.