To provide a manufacturing method of a cylinder head, by which cooling water housed in a water space of the cylinder head can sufficiently cool particularly a combustion chamber in the lower range of the cylinder head with a simple means.

In the manufacturing method of the cylinder head in an internal combustion engine in a mold 1 by casting, a cavity 5 for forming the cylinder head is remained at the interval between an upper mold 2 and a lower mold 3. A sand core 8 for forming the water space for cylinder head, is inserted into the mold 1. A rejecting body 10 is incorporated into the sand core 8 for water space before the casting process, and left in the water space after the casting process.