PURPOSE: To constitute the molding method so that a hole part of a rocker arm is formed into a right circle without deforming an insert bushing, by a method wherein the circumference of the insert bushing, which is set up so that it is fitted over an axial protrusion on the inside of a mold, is filled with a molding material.

CONSTITUTION: A mold 1 is made into a broken state by moving a movable retainer plate 2 of the mold 1 along with an axial protrusion and ejection pin 5 by a mold clamping device and insert bushing 12 is set up so that an insert bushing 12 is fitted over an axial protrusion 4. Then the mold 1 is closed and a molding material is filled into the mold 1 through a gate 6. As a result of heating and expansion of an axial protrusion 4 by electrifying an electric heating wire 4a, the outside diameter is expanded, a gap is eliminated between the axial protrusion 4 and the insert bushing 12 and presses the insert bushing 12 in the direction of spreading out the same. Therefore, this pressing force opposes against injection pressure or pressure from the ejection pin 5 and worsening of a degree of right circle of the insert bushing 12 is prevented. Then after solidification of a rocker arm 11, cooling water is passed through a cooling passage 4b and the outside diameter of the axial protrusion is reduced.