A set screw (56) is provided, which has a screw main body (71), a male thread portion (75) which is formed on an outer periphery of the screw main body (71), and a drain hole (78) which penetrates a central portion of the screw main body (71) in an extension direction of the screw main body (71). The blade root ring (53) has a hole (63) which extends radially outward from an inner peripheral surface (53a) of the blade root ring (53), and a female thread portion (64) which is formed on an inner peripheral surface (63a) of the hole (63), and the set screw (56) is screwed into the female thread portion (64).