The invention proposes a belt pulley decoupler (101, 201, 301, 401) for transmitting drive torque from the belt of an auxiliary unit belt drive to the shaft of one of the auxiliary units, comprising: - a belt pulley (2), - a hub (4) to be mounted on the shaft, - a first sleeve (114, 214, 314, 414), which is rotationally fixed in the pulley, - a second sleeve (15), which is rotatable in the pulley, - and a series connection of a decoupler spring (12) and a wrap-around band (111, 211, 311, 411) disposed in the drive torque flow between the belt pulley and the hub. The wrap-around band ends, which couple the two sleeves to one another non-rotatably while transmitting the drive torque, extend the wrap-around band radially. One of the two sleeves has a circumferentially extending slot (119, 219) and the wrap-around band end coupled to this sleeve is configured as a limb (120, 220), which interlockingly engages in the slot non-rotatably in the direction of rotation of the drive torque.