A gas turbine airfoil assembly 300), comprising: an inner band end wall portion provided at an inner circumferential, turbine-radial inside, end portion of the gas turbine airfoil and an outer band end wall portion provided at an outer circumferential, turbine-radial outside, end portion of the gas turbine airfoil; wherein the two end wall portions (100, 200) constitute part of a gas path of a gas turbine; an airfoil portion arranged between the inner and outer band end wall portions (100, 200) and having a cooling passage therein; an opening portion disposed in the inner band end wall portion, through which cooling air can pass from the cooling passage in the airfoil portion to an internal cooling passage in an inner diaphragm ring; an upstream-side hook portion • provided on an inner circumferential surface of the inner band end wall portion located on the turbine-radial inside so as to secure the inner band end wall portion to the diaphragm inner ring, and • projecting from the inner circumferential surface of the end wall portion toward the turbine-radial inside; and a plurality of cooling holes (130; 131) disposed in the upstream-side hook portion so as to be connected to the cooling passage in the airfoil portion, wherein the plurality of cooling holes (130; 131) is provided: • in a circumferential direction of the gas turbine; • at each of a first area, located between a point (Pb), at which a plane including the central axis of the gas turbine is in contact with a suction side of the airfoil portion, and a middle point (Pm) between a position (Pt) of the trailing edge and a position of the leading edge of the airfoil portion in the circumferential direction of the gas turbine, and a second area, located between the middle point (Pm) and the position (Pt) of the trailing edge; and • in intervals, characterised in that the intervals in circumferential direction are narrower in the first area than in the second area. an inner band end wall portion provided at an inner circumferential, turbine-radial inside, end portion of the gas turbine airfoil and an outer band end wall portion provided at an outer circumferential, turbine-radial outside, end portion of the gas turbine airfoil; wherein the two end wall portions (100, 200) constitute part of a gas path of a gas turbine; an airfoil portion arranged between the inner and outer band end wall portions (100, 200) and having a cooling passage therein; an opening portion disposed in the inner band end wall portion, through which cooling air can pass from the cooling passage in the airfoil portion to an internal cooling passage in an inner diaphragm ring; an upstream-side hook portion • provided on an inner circumferential surface of the inner band end wall portion located on the turbine-radial inside so as to secure the inner band end wall portion to the diaphragm inner ring, and • projecting from the inner circumferential surface of the end wall portion toward the turbine-radial inside; and • provided on an inner circumferential surface of the inner band end wall portion located on the turbine-radial inside so as to secure the inner band end wall portion to the diaphragm inner ring, and • projecting from the inner circumferential surface of the end wall portion toward the turbine-radial inside; and a plurality of cooling holes (130; 131) disposed in the upstream-side hook portion so as to be connected to the cooling passage in the airfoil portion, wherein the plurality of cooling holes (130; 131) is provided: • in a circumferential direction of the gas turbine; • at each of a first area, located between a point (Pb), at which a plane including the central axis of the gas turbine is in contact with a suction side of the airfoil portion, and a middle point (Pm) between a position (Pt) of the trailing edge and a position of the leading edge of the airfoil portion in the circumferential direction of the gas turbine, and a second area, located between the middle point (Pm) and the position (Pt) of the trailing edge; and • in intervals, characterised in that the intervals in circumferential direction are narrower in the first area than in the second area. • in a circumferential direction of the gas turbine; • at each of a first area, located between a point (Pb), at which a plane including the central axis of the gas turbine is in contact with a suction side of the airfoil portion, and a middle point (Pm) between a position (Pt) of the trailing edge and a position of the leading edge of the airfoil portion in the circumferential direction of the gas turbine, and a second area, located between the middle point (Pm) and the position (Pt) of the trailing edge; and • in intervals, characterised in that the intervals in circumferential direction are narrower in the first area than in the second area.