A concave (a relief portion) 20 is formed along a circumferential direction of a rotor in a trailing-edge end surface 18 of a platform 16. In the trailing-edge end surface 18 disposed outside of the relief portion 20 in the radial direction of the rotor, provided is an opening 15 of a cooling channel 14. The end surface 18 is formed thicker in the radial direction of the rotor at the opening of the cooling channel 14 than at a position corresponding to a trailing-edge end of the a hub 13 of a aerofoil portion 12 connected to the platform.