Center cores are formed by
extrusion-molding ABS resin. Seven pieces of the center cores, which are juxtaposed to each other in the horizontal direction, are supplied by a pultruder, and reinforcing long-fibers impregnated with an
unsaturated polyester resin are allowed to pass through dispersion guides and squeezing nozzles, to thus squeezing-mold a
fiber-reinforced composite hollow structure having FRP made legs. A final squeezing
nozzle is disposed in a cross head die through a cooling jacket, and the hollow structure thus molded is allowed to pass therethrough to be covered with the ABS resin in a state in which the outer periphery of the hollow structure is heated. The hollow structure thus covered is subjected to cooled-
sizing through a plurality of
horizontal and vertical pairs of rollers, and then cured in a hot curing tank. The surface covered with the ABS resin is subjected to a surface-treatment of imparting irregularities for giving an antislipping function to the surface. A
thermoplastic resin-made protective cap is fitted to an end of the center core. The apparatus for manufacturing a composite hollow structure has a plurality of pairs of rotatable and heat-resisting
sizing rollers. The plurality of pairs of the
sizing rollers are disposed in the pultruding direction while being gradually cooled in the order from those positioned on the upstream side to those positioned on the downstream side for sizing the softened outer layer covering the outer periphery of the intermediate layer.