PURPOSE: To provide a method for obtaining the good formability, restraining heating temp, in forging as lower as possible while avoiding lowering of the strength caused by thermal effect in the case of manufacturing a member of a wheel, etc., for bicycle with an Mg alloy, particularly, in the case of applying the forging to a part of this casting stock.

CONSTITUTION: By embedding a chillier 23 at position corresponding to the outer peripheral surface of a rim part in a cavity having the shape of the almost corresponding to the wheel shape as the finish product, at the time of forming the casting stock by using a mold, the above rim part is rapidly cooled and thereafter this rapidly cooled part is heated at 270°C and the forging is executed.