PURPOSE: To prevent the defective packing of shell sand and to obtain a cam shaft having a good casting surface by forming the prescribed part of the cams of the cam shaft by blow molding and the other parts by dump molding and casting the cam shaft by combining both.

CONSTITUTION: A half-split casting mold adjacently disposed with chillers 2, 3 respectively corresponding to cams C1, C2 so as to be partially superposed when viewed from the axial line direction of the cam shaft is formed as a partial shell core 5 by blow molding. On the other hand, a half-split master mold 8 having recesses 8a, 8b, 8c which can be fitted with the partial shell cores 5, 5... is formed by dump molding. Then the shell cores 5, 5... of the half-split parts are fitted in the prescribed attitude into the recesses 8aW8c of the master mold 8 to form one of the half-split shell molds 9. The other split shell mold 10 is similarly formed. Both molds 9, 10 are mated to form a shell mold and thereafter a molten metal is poured into the mold, by which the cast cam shaft C is obtd.