The utility model relates to a hub unit bearing for supporting a wheel of an automobile in a free rotating manner relative to a suspension device. The inner seal member includes an inner seal ring having an inner seal portion, an inner slinger, and an encoder made of magnetic rubber and supported by the inner slinger. The outer seal member includes an outer seal ring having an outer seal portion formed in a cross-sectional shape in which the inner seal portion is turned over, an outer slinger, and a non-magnetic rubber encoder equivalent portion formed in a cross-sectional shape in which the encoder is turned over and supported by the outer slinger. The radial inner side part of the encoder equivalent part is in close contact with the axial inner side surface of the rotating flange in thewhole circumferential range, so that the development cost of the sealing part is inhibited, and water is prevented from entering the space between the rotating flange and the outer oil slinger.