A gas turbine blade having a platform and a turbine wheel plate, in which cooling passages are arranged in a plurality of rows and connected to one another in a blade trunk section of a moving blade and a supply-side passage and a discharge-side passage are formed in a blade root section. The gas turbine blade comprises a pocket having an inlet and an outlet formed in the blade root section. The supply-side passage is connected to one of the cooling passages and the inlet of the pocket, the outlet of the pocket is connected to another of the cooling passages, and the discharge-side passage is connected to one of the cooling passages other than the ones connected individually to the supply-side passage and the pocket.