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).