A pulley device for a tensioner roller or winding roller of a transmission element, having a pulley, a bearing, and an annular protective flange. The flange provides a first radial portion of small diameter, the first radial portion bearing against a fixed inner ring of the bearing, a second radial portion of large diameter, and a substantially axial intermediate portion connecting the first and second radial portions. The intermediate portion forms a circumferential trough, the bottom of which is offset radially towards the inside of the pulley device compared with the outer edge of the fixed inner ring.