An isolation damper pulley comprises a damper section 1 and an isolation pulley section 2 assembled thereto, wherein a first fitting portion 18 constituted from a cylindrical portion concentric with a center axis O of a through hole 13 is provided to a hub 10 of the damper unit 1. The isolation pulley section 2 has a supporting member 22 fixed to a pulley portion 21 via an annular elastic member 23, wherein a second fitting portion 27 concentric with the first fitting portion 18 is provided to the supporting member 22. A third fitting portion 32 concentric with the first fitting portion 18 is provided to a pressing member 31 applying a precompression to the annular elastic member 23 in cooperation with the supporting member 22. The second fitting portion 27 and the third fitting portion 32 are fitted to each other and these fitting portions are fitted to the first fitting portion 18, so that the isolation pulley section 2 is assembled to the damper section 1.