PURPOSE: To perform engagement naturally and transmit rotational torque enough by forming an engaging part of resin foam agent, coppresponding to an engaged part of an end member on an end of a cylindrical member.

CONSTITUTION: A resin foam agent 1 is charged in an inner periperal end of a cylindrical member 4 through a foaming material injector 6, while a molding jig 7 is fitted to the end of the cylindrical member 4. An outside dimension guide 8 is engaged with an outer periphery of the cylindrical member 7 in order to measure of an outer periphery reference of the cylindrical member 4. A center part forming pin 7a and a supporting part forming pin 7b are set with the outside dimension guide 8 being a reference. After the molding jig 7 is fitted to the end of the cylindrical member 4 and the resin foam agent is hardened, the molding jig 7 is retreated and an engaging part, composed of a center part installing hole 2 and a rotational direction supporting hole 3, corresponding to an engaged part of an end member is formed on the cylindrical member 4.