A friction stir welding method includes a first friction stir welding process of forming a first stirring region in a beveled part, by moving a first rotary tool disposed on an upper side in a thickness direction across the beveled part, while rotating the first rotary tool; and a second friction stir welding process of forming a second stirring region in the beveled part, by moving a second rotary tool disposed on a lower side in the thickness direction across the beveled part, while rotating the second rotary tool, simultaneously with the first friction stir welding process or after performing the first friction stir welding process.