A friction stir welding device for welding an article by means of a welding tool, includes: a tool holding section configured to hold the welding tool and rotate round a predetermined reference axial line; rotation driving unit configured to drive the tool holding section to rotate round the reference axial line; movement driving unit configured to drive the tool holding section to move along the reference axial line; and a car body loaded with the tool holding section, the rotation driving unit and the movement driving unit, the car body being configured to travel above or below the article.