PURPOSE: To form ringlike reinforcing ribs of rigid resin on the periphery of a hose by operating a slitter, molds and a soft hose in conjunction with one another.

CONSTITUTION: After rigid resin A is poured for a certain time onto the periphery of a soft hose H inserted in a slitter 4 from a gap (b) between a die 1 and a nippled 2 by an extrusion machine 3, the slitter 4 is moved downward and the resin A is cut by a blade 4a while being extruded out from the die 1. On this occassion, the resin A is pushed into ringlike recesses (d) of a plurality of molds 6 for reforming reinforcing ribs, which are provided below the die 1. Thus, ringlike reinforcing ribs B are formed on the periphery of the hose H by operating the blade 4a in response to the positions of the recesses (d). Each rib B is lowered by a distance corresponding to a piece of a mold in the state where the slitter 4 is in contact with the mold 6, and cooled. Then, the slitter 4 is raised up and the next piece of a mold 6 is inserted into the space opened because of this movement. Each piece of the mold 6 is returned to its original position after being used to reform and cool the respective rib (B).