The invention belongs to a broadband multi-waveguide output device for a rotary traveling wave tube. The broadband multi-waveguide output device comprises a circular waveguide, long stripped rectangular waveguides and rectangular coupling holes, wherein the circular waveguide is provided with an input opening and an output opening, the long stripped rectangular waveguides are arranged on a circular waveguide casing at intervals in the axial direction and are provided with microwave output openings, the rectangular coupling holes are arranged between the circular waveguide and the rectangular waveguides, the axial lengths of all holes are identical, the center distances among all holes are identical, the widths of four front holes at two ends of each group of rectangular holes are in step-type arrangement from narrow to wide, the width of each hole in the middle is the same as the width of the fourth hole at the two ends, and in addition, an inclined coupling surface is also arranged at the junction part of each rectangular waveguide inner cavity front end surface and the circular waveguide. The multi-waveguide output device has the characteristics that the requirements of the millimeter band of high power, high gain and high frequency band for being matched with the rotary traveling wave tube to be used can be sufficiently met, the base parameters are provided for the optimization design of voltage reduction collection electrodes, and the like. The defects of narrow band width, matching use difficulty with the broadband rotary traveling wave tube, and the like in the prior art are overcome.