A blade of a gas turbine includes a main body having a dovetail portion and a blade portion extending from the dovetail portion. A cooling air passage for flowing a cooling air is formed in the main body to cool the blade portion. The passage includes a cooling air inlet port open to the dovetail portion and an outlet port open to an extended tip of the blade portion. A first passage portion extends from the inlet port to the portion close to the extended tip along a leading edge of the blade portion. A final passage portion extends from the dovetail portion to the outlet port. The flow sectional area of the final passage portion is gradually decreased from the dovetail portion toward the outlet port. The final passage portion communicates with a number of film cooling holes which are open to the suction side surface of the blade portion.
