To provide a wheel supporting bearing unit with a seal having excellent durability, in which sealability by a seal ring is improved, thus further improving the preventive effect against intrusion of foreign mattaer into the inside space.

An eaves lip 21a is arranged radially outward than a seal lip 19a arranged on the radial outermost side, and the whole is formed in a substantially cylindrical shape by extending to both sides in the axial direction from the outer diameter side edge of a circular ring part 23a, and a venturi mechanism is constituted by arranging an inflow part 30a, an orifice part 31a and an outflow part 32a of air in this order from the inside in the axial direction. A plurality of through-holes 35a communicating with an orifice from an inflow port are arranged in the circumferential direction by penetrating in the axial direction through the circular ring part 23a and a sealant 18a on the inner diameter side of the orifice part 31a, the orifice part 31a is superimposed in the radial direction on an annular clearance 27, and the air can flow between the orifice of the orifice part 31a and the annular clearance 27.