A joining method providing improved joining accuracy for wheel and turbine shaft. A part of the inner peripheral wall of a fitting hole of a wheel is tapered inwardly from the opening of the fitting hole. At one end of the turbine shaft to be joined to the wheel, a tapered axial abutment portion is provided. In the turbine shaft, an axial abutment portion is provided in a part other than the portion to be fused by welding to suppress deformation at the time of fusion. The axial abutment portion is tapered, and the inner peripheral wall of the fitting hole is tapered, whereby the wheel and the turbine shaft are brought into close contact with each other while positioned coaxially. As such, close contact is effected in a stable manner in the axial abutment portion where tapered surfaces come into contact with each other.