A crankshaft supporter having a bearing holder molded in aluminum alloy and having a bearing for supporting a crankshaft. A preform member is cast inside of the aluminum alloy. A screw hole having one opened end is formed in an outer surface of the bearing holder. A concave recess section is formed in the preform member to accommodate a bottom of the screw hole. An introduction passage is provided in the recess section to introduce molten metal therein during casting to prevent blowholes.