To prevent the deformation and breakage of the core itself upon casting by improving the strength of a core itself, to reduce a production error by improving the production precision of a serpentine passage in a turbine blade, and to reduce production cost and improve the productivity of turbine blade production by enhancing the production yield of the turbine blade.

The core 31 for producing the turbine blade, which is used when the turbine blade having a serpentine passage at the inside is produced by casting, is provided with a first cooling medium passage forming part 32 and a second cooling medium passage forming part 33, which form the serpentine passage. The first cooling medium passage forming part 32 and the second cooling medium passage forming part 33 are connected to each other through a first connection part 40.