A plate (13(e)), the outer diameter side of which is fixed to be integral with a plate section (13c), and which is provided with an engagement part (13g) to be engaged with a shoulder (13f) formed on the inner diameter side of a boss section (13a), is integral with a center hub (13). Thereby, even if a bridge section (13d) is broken and the plate section (3c) moves in the detachment direction of the center hub (13), the engagement part (13g) of the plate (13e) is engaged with the shoulder (13f) of the boss section (13a), whereby the plate section (13c) and the boss section (13a) are engaged and coupled with each other while interrupting the torque transmission. Accordingly, even if the bridge section (13d) is broken, the boss section (13a) as well as the plate section (13c) side are prevented from being detached from a pulley (10).