The present invention relates to a dragging device for restricting the one-way rotation of a spool of a fly reel. In a rotation-restricting device of a spool of a fly reel having a dragging device which can allow the spool to be attached to and detached from a shaft secured to a housing and which can restrict the one-way rotation of the spool, a sleeve is fitted on the shaft secured to the housing, a flange extends in the radial direction from one end of the sleeve, a flange cover is secured to the housing in the spool-attached direction, the flange makes contact between the flange cover and the housing, and a disk plate makes contact with the flange, whereby the pressure applied due to the rotation of a drag-adjusting knob mounted on the outside of the housing is transferred to the disk plate to be able to restrict the one-way rotation of the spool. In addition, a waterproof structure is provided on the friction surface of the disk plate to prevent infiltration of water.
