A sealing device for sealing between a through-hole and a shaft inserted through the through-hole, the sealing device comprising: a reinforcing ring formed annularly around an axis (x); and an elastic body part formed from an elastic body that is attached to the reinforcing ring and that is formed annularly around the axis, the elastic body part including: an annular seal lip for being in contact with the shaft such that the shaft is slidable; an annular dust lip, the dust lip being provided on an outer side (a) of the seal lip and extending toward the axis; and an annular side lip, the side lip extending toward the outer side on an outer periphery side (c) of the dust lip, the side lip having: an annular middle portion, the middle portion increasing in diameter as progress toward the outer side in a direction of the axis; and an annular distal end portion, the distal end portion being a portion connected to and on the outer side of the middle portion, the distal end portion increasing in diameter as progress toward the outer side in the direction of the axis, wherein, in the side lip, the distal end portion is bent to an inner periphery side (d) from the middle portion, characterized in that; the distal end portion of the side lip is formed so as to decrease in thickness as progress toward the middle portion side; and, in the middle portion, at least one groove is formed annularly around the axis. a reinforcing ring formed annularly around an axis (x); and an elastic body part formed from an elastic body that is attached to the reinforcing ring and that is formed annularly around the axis, the elastic body part including: an annular seal lip for being in contact with the shaft such that the shaft is slidable; an annular dust lip, the dust lip being provided on an outer side (a) of the seal lip and extending toward the axis; and an annular side lip, the side lip extending toward the outer side on an outer periphery side (c) of the dust lip, the side lip having: an annular middle portion, the middle portion increasing in diameter as progress toward the outer side in a direction of the axis; and an annular distal end portion, the distal end portion being a portion connected to and on the outer side of the middle portion, the distal end portion increasing in diameter as progress toward the outer side in the direction of the axis, an annular seal lip for being in contact with the shaft such that the shaft is slidable; an annular dust lip, the dust lip being provided on an outer side (a) of the seal lip and extending toward the axis; and an annular side lip, the side lip extending toward the outer side on an outer periphery side (c) of the dust lip, the side lip having: an annular middle portion, the middle portion increasing in diameter as progress toward the outer side in a direction of the axis; and an annular distal end portion, the distal end portion being a portion connected to and on the outer side of the middle portion, the distal end portion increasing in diameter as progress toward the outer side in the direction of the axis, an annular middle portion, the middle portion increasing in diameter as progress toward the outer side in a direction of the axis; and an annular distal end portion, the distal end portion being a portion connected to and on the outer side of the middle portion, the distal end portion increasing in diameter as progress toward the outer side in the direction of the axis, wherein, in the side lip, the distal end portion is bent to an inner periphery side (d) from the middle portion, characterized in that; the distal end portion of the side lip is formed so as to decrease in thickness as progress toward the middle portion side; and, in the middle portion, at least one groove is formed annularly around the axis.