To provide a friction stir welding method for simultaneously solving such conventional problems that a decrease in strength due to material perforation and insufficient stirring, a decrease in productivity due to abnormal stop of welding equipment, and deterioration in quality due to defective appearance.

When performing the friction stir welding of materials 1, 2, the adequate numbers of target positions are specified at arbitrary positions in the overlapping direction of the materials 1, 2, and the positional control of a welding tool 3 is performed by setting the welding condition of the welding time, the pressure, and the number of rotation for each positional control range to be classified in the overlapping direction by the target positions. When the position of a fore end of the welding tool 3 reaches the target position earlier than the welding time set in the positional control range, the present target position is maintained before the remaining welding time is elapsed. In the mean time, when the position of the fore end of the welding tool 3 does not reach the target position even if the welding time set in the positional control range is elapsed, the welding time is prolonged until the fore end reaches the target position.

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