To provide a high quality sand core having improved density and strength due to good filling properties.

A predetermined amount of casting sand 25 is filled in a molding drum 6 to rotate the molding drum 6. In a state that the casting sand 25 is evenly spread to the whole inner peripheral surface of a cavity 12 by centrifugal force, a plate 22 is advanced and amine gas is sprayed from a nozzle 23, thereby curing the inside surface of the casting sand 25. Then, the rotation of the molding drum 6 is suspended, the plate 22 is advanced to seal the cavity 12, thereby blowing off the vaporized amine gas from the nozzle 24 together with compressed gas. As a result, high-pressure vaporized gas blown off inside the cavity 12 is radially discharged from each vent hole through the casting sand 25, so as to cure the whole casting sand 25. After the completion of curing, a molded casting sand 26 can be taken out by releasing a mold.