An elastic body includes an annular main body portion to be disposed in an annular gap, a seal lip portion extending from a portion, closer to an object to be sealed, of the main body portion and being to be in contact with an inner member, a flange portion extending outwardly from an end, opposite to the object to be sealed, of the main body portion and including a first side closer to the object to be sealed, the first side being to be in contact with an outer member, a side lip portion extending from the end opposite to the object to be sealed in a direction away from the object to be sealed, and a projecting portion formed circumferentially on a second side, opposite to the object to be sealed, of the flange portion. The side lip portion has a back surface configured to be in contact with the projecting portion in response to the side lip portion being pressed by a mating member disposed opposite to the object to be sealed.