The present invention furnishes a seal structure able to equalise an elastic contact pressure. A seal element 22 is secured in an annular groove 21 formed on an external lateral surface of a portion of support hub 20a. There is provided a flange portion 24 of a cup type seal 23 mounted so as to cover the external lateral surface of the portion of support hub 20a. A first lip 32 formed as part of the seal element 22 enters elastically into contact with a portion of main body of the cup seal 23 in the direction of thrusting, and a second lip 33 enters elastically into contact with the flange portion 24 in the radial direction. Even when the cup seal 23 is displaced with relative motion in the vertical direction, the elastic contact pressure can be equalised.