Abstract: It is an object of the present invention to provide a retainer cone that, by internally inserting the retainer cone into the central portion at the upper end portion of the retainer main body, which is an area, where negative pressure is generated, in the vicinity of the attaching portion of a prior art venturi tube, is capable of dispersing a part of the compressed air jetted from a nozzle at the upper part of the retainer main body, when carrying out reverse air filtration of a filtration fabric, in the radius direction of the retainer main body, preventing negative pressure from being generated at the upper end side of the retainer main body, outwardly inflating the entire filtration fabric including the upper end side of the retainer main body, securely shaking off powder dust adhered to the filtration fabric, and simultaneously enlarging the sectional area of a flow path at the upper end portion of the retainer main body in comparison with a prior art venturi type, and significantly reducing the load of