Turbine stator vane and gas turbine

A turbine stator vane comprising:

• an airfoil portion;
• an inner shroud that is provided inside the airfoil portion in a vane height direction;
• a pair of circumferential wall portions that extends, at end portions of the inner shroud on one side and the other side in a circumferential direction, along a direction in which the end portions extend and that protrudes from the inner shroud toward an opposite side to the airfoil portion in the vane height direction;
• a longitudinal wall portion that extends in the circumferential direction such that end portions on the one side and the other side in the circumferential direction are connected to the pair of circumferential wall portions, that protrudes from the inner shroud toward the opposite side to the airfoil portion in the vane height direction, and that protrudes to be closer to the opposite side in the vane height direction than the pair of circumferential wall portions is;
• a connecting portion that connects the pair of circumferential wall portions and the longitudinal wall portion to each other via a gently curved surface;
• and
• a first plate member that forms a cavity together with a surface of the inner shroud on the opposite side and the pair of circumferential wall portions,
• wherein the first plate member includes a first planar portion extending along the pair of circumferential wall portions, a second planar portion extending along the longitudinal wall portion, and a curved surface portion extending along the connecting portion, and
• the curved surface portion includes thick portions of which a thickness is larger than thicknesses of the first planar portion and the second planar portion, the thick portions being provided at at least end portions on the one side and the other side in the circumferential direction.