A blade (50;50b;50c;50d;50e) comprising: a blade body that forms an airfoil and is to be disposed inside a combustion gas flow passage through which combustion gas flows in operation; a platform that spreads from an end in a blade height direction (Dwh) of the blade body in a direction having a component perpendicular to the blade height direction (Dwh); and a shaft-mounted part that extends from the platform toward the opposite side from the blade body, wherein a blade passage through which cooling air flows in operation is formed inside the blade body, the platform, and the shaft-mounted part so as to extend through the blade body, the platform, and the shaft-mounted part in the blade height direction (Dwh), the platform has a gas path surface that faces the blade height direction (Dwh) and comes in contact with the combustion gas in operation, a shaft-side surface that is located back-to-back with the gas path surface, and a platform passage which is formed between the gas path surface and the shaft-side surface and through which cooling air flows in operation, the blade (50;50b;50c;50d;50e) has a communication passage (75;75b;75c;75d;75e) that leads from at least one surface of the shaft-side surface of the platform and an outer surface of the shaft-mounted part through the platform passage to the blade passage, an opening of the communication passage (75;75b;75c;75d;75e) in the at least one surface is blocked with a sealing member, the platform passage has an inflow passage portion (82;82n;82p) that extends from a position near the blade passage in a direction having a component of a blade thickness direction (Dwt) based on that position, an inner surface defining the inflow passage portion (82;82n;82p) includes a gas path-side inner surface that faces the shaft-side surface side, and a shaft-side inner surface that is the only surface of the inner surface facing the gas path-side inner surface and spreads in a direction having more of a component of the blade thickness direction (Dwt) than a component of the blade height direction (Dwh), and an inner surface defining the communication passage (75;75b;75c;75d;75e) intersects with and joins to the shaft-side inner surface of the inflow passage portion (82;82n;82p). a blade body that forms an airfoil and is to be disposed inside a combustion gas flow passage through which combustion gas flows in operation; a platform that spreads from an end in a blade height direction (Dwh) of the blade body in a direction having a component perpendicular to the blade height direction (Dwh); and a shaft-mounted part that extends from the platform toward the opposite side from the blade body, wherein a blade passage through which cooling air flows in operation is formed inside the blade body, the platform, and the shaft-mounted part so as to extend through the blade body, the platform, and the shaft-mounted part in the blade height direction (Dwh), the platform has a gas path surface that faces the blade height direction (Dwh) and comes in contact with the combustion gas in operation, a shaft-side surface that is located back-to-back with the gas path surface, and a platform passage which is formed between the gas path surface and the shaft-side surface and through which cooling air flows in operation, the blade (50;50b;50c;50d;50e) has a communication passage (75;75b;75c;75d;75e) that leads from at least one surface of the shaft-side surface of the platform and an outer surface of the shaft-mounted part through the platform passage to the blade passage, an opening of the communication passage (75;75b;75c;75d;75e) in the at least one surface is blocked with a sealing member, the platform passage has an inflow passage portion (82;82n;82p) that extends from a position near the blade passage in a direction having a component of a blade thickness direction (Dwt) based on that position, an inner surface defining the inflow passage portion (82;82n;82p) includes a gas path-side inner surface that faces the shaft-side surface side, and a shaft-side inner surface that is the only surface of the inner surface facing the gas path-side inner surface and spreads in a direction having more of a component of the blade thickness direction (Dwt) than a component of the blade height direction (Dwh), and an inner surface defining the communication passage (75;75b;75c;75d;75e) intersects with and joins to the shaft-side inner surface of the inflow passage portion (82;82n;82p).