Storage device for a plant for winding reels of web-like material, which comprises: - a support structure provided with: - a base intended to be abutted against the ground, - at least one support frame placed on the upper part and spaced with respect to said base; - a movable trolley slidably connected to said support structure and movable between a work configuration, in which said movable trolley is placed in proximity to said base of said support structure, and a storage configuration, in which said movable trolley is placed in proximity to said support frame of said support structure; - a first series of first transmission rollers rotatably mounted on said support structure at said base; - a second series of second transmission rollers rotatably mounted on said movable trolley and arranged substantially parallel to said first series of the first transmission rollers; said web-like material being intended to alternately pass between the first transmission rollers and the second transmission rollers in order to be stored between said base of said support structure and said movable trolley with the latter moved from the work configuration to the storage configuration; said storage device also comprising: - a plurality of transmission pulleys rotatably mounted on the support frame of said support structure; - movement means for rotating said first transmission rollers and said second transmission rollers, comprising at least one elongated flexible element closed as a ring and at least partially wound around the first transmission rollers of said first series, the second transmission rollers of said second series and said plurality of transmission pulleys; - at least one motor mechanically fixed to said support structure and fit to a drive pulley at least partially enclosed by said elongated flexible element in order to move each single roller of said first transmission rollers and second transmission rollers (6, 9); said storage device being characterized in that said elongated flexible element is a cable, a wire, a cord or a web and in that it comprises tensioning means mechanically associated with said elongated flexible element in order to adjust the tension thereof in an automatic manner. - a support structure provided with: - a base intended to be abutted against the ground, - at least one support frame placed on the upper part and spaced with respect to said base; - a base intended to be abutted against the ground, - at least one support frame placed on the upper part and spaced with respect to said base; - a movable trolley slidably connected to said support structure and movable between a work configuration, in which said movable trolley is placed in proximity to said base of said support structure, and a storage configuration, in which said movable trolley is placed in proximity to said support frame of said support structure; - a first series of first transmission rollers rotatably mounted on said support structure at said base; - a second series of second transmission rollers rotatably mounted on said movable trolley and arranged substantially parallel to said first series of the first transmission rollers; - a plurality of transmission pulleys rotatably mounted on the support frame of said support structure; - movement means for rotating said first transmission rollers and said second transmission rollers, comprising at least one elongated flexible element closed as a ring and at least partially wound around the first transmission rollers of said first series, the second transmission rollers of said second series and said plurality of transmission pulleys; - at least one motor mechanically fixed to said support structure and fit to a drive pulley at least partially enclosed by said elongated flexible element in order to move each single roller of said first transmission rollers and second transmission rollers (6, 9); said storage device being characterized in that said elongated flexible element is a cable, a wire, a cord or a web and in that it comprises tensioning means mechanically associated with said elongated flexible element in order to adjust the tension thereof in an automatic manner.