To prevent mud or the like from infiltrating by the structure curtailed in the breadwise width of the pulley, and also to curtail the breadthwise size of the pulley unit as a whole.

The pulley unit is constituted of a pulley 1, a shaft body 2 to be relatively rotatable to the pulley 1 and coaxially arranged in the inside of the pulley 1, a one way clutch 3 interposed in the annular space S between the pulley 1 and the shaft body 2, and a rolling bearing 5 provided at the side of the one way clutch 3 in the annular space S. Further, the pulley unit is provided with an annular seal 6 by which the axial outside of the rolling bearing 5 positioning in the annular space S and hermetically sealing the axial outside of the rolling bearing 5, and a thin plate member 8 fixed in one side of the shaft body 2 and the pulley 1 and provided extendingly over both end faces of the pulley 1 and the shaft body 2 to at least cover the annular space S.