To provide a crankcase casting mold by which a crankcase can be cast at a low cost with the same mold, even when the model of a small-sized car on which an internal combustion engine is mounted, is changed, by changing the position of the insert in the mold of the crankcase of the internal combustion engine.

The casting mold 40 of a crankcase 11 is equipped with a rear fork pivotally supporting structure in which a rear fork 18 is pivotally supported so as to be rockable vertically on one pivot 19 that penetrates in the right and left direction the rear part 11a of the right/left crankcases of the internal combustion engine 10 to be mounted on the small-sized car. The casting mold 40 includes: an upper mold 41 that forms the exterior of the crankcase 11 and an insert fitting hole 43 in which the base 47 of the insert 46 is fitted; a lower mold 44 that forms the interior of the crankcase 11; and an insert equipped with a column part 48 of a pivot supporting hole projecting into the crankcase, while shifting the position from the center of the base 47 of the insert 46 that is fitted to the insert fitting hole 43 of the upper mold 41.