An airfoil of either of a turbine blade or a turbine vane includes a cooling passage; at least one disk body disposed on an inner wall of the cooling passage and configured to reduce a flow cross-sectional area of the cooling passage to increase a fluid pressure of cooling fluid flowing through the cooling passage; and at least one through-hole formed in each of the at least one disk body such that the cooling fluid flows through the at least one through-hole and forms a vortex on a downstream side of the at least one through-hole. The cooling passage includes an inlet supplied with the cooling fluid and an end opposite to the inlet, and the at least one disk body is disposed at the inlet of the cooling passage and is configured to increase the fluid pressure of the cooling fluid flowing into the cooling passage.