A concave (a relief portion) is formed along a circumferential direction of a rotor in a trailing-edge end surface of a platform. In the trailing-edge end surface disposed outside of the relief portion in the radial direction of the rotor an opening of a cooling channel is provided. The end surface is formed thicker in the radial direction of the rotor at the opening of the cooling channel than at a position corresponding to a trailing-edge end of a hub of an airfoil portion connected to the platform.