Core molding method and core molding device

A core molding method for molding a core having a helical shape using a core die, the method comprising:

• a hardening step in which the core die is disposed in a frame and then self-hardening sand acquired by mixing sand, a resin, and a hardener is filled into the frame and left to harden;
• and
• a die removal step in which the core die is removed from the core, resulting from hardening of the self-hardening sand, while being rotated around an axis of the core die,
• wherein, in the die removal step, a time for hardening the self-hardening sand, a frictional force exerted between the core and the core die during die removal, and strength of the core during die removal are optimized.