The present invention provides an apparatus for manufacturing bellows which contributes to expand the life of the resin bellows to be used for vehicles and to improve the quality of the same. The apparatus for manufacturing bellows comprises a nozzle body including an annular passage and a nozzle port formed by the annular nozzle mouthpiece and the nozzle core, and a neck die having a pin and an outer surrounding body on the opposite side of the nozzle body in which the outer surrounding body abuts against the nozzle mouthpiece and the end portion of the pin projecting from the outer surrounding body abuts against the nozzle core to form a cavity for molding the neck portion in communication with the nozzle port between the pin and the outer surrounding body prior to manufacturing of the bellows, and moves away from the state being abutted against the nozzle body with the resin portion filled in the cavity crimped when manufacturing the bellows, wherein the extent of projection of the end of the pin from the outer surrounding body is determined so that the nozzle core is allowed to be displaced in the axial direction while maintaining the state being abutted against the end portion, and the boundary portion between said neck portion and the bellows body is able to be increased in thickness and quantity when filling resin into said cavity.