The present invention concerns a reel seat holding device for a movable reel and reel seat assembly for fly fishing rods. The holding device comprises a case that is arranged for releasably receiving the reel seat therein, when the reel and reel seat assembly is detached from a fly fishing rod. A device is provided for mounting the case on a fishing rod or an holder. The disclosure of the present invention also relates to a fly fishing rod with a movable reel and reel seat assembly and a waist holder for the holding device.