Friction stir welding device and friction stir welding method

A friction stir welding device (1) is provided with: a stage (3) that has a loading surface (31) on which a workpiece (9) is loaded and that is rotatable about a stage rotation axis (C2) intersecting the loading surface (31); a tool holder (10) that is movable relative to the table (3) in a direction along the loading surface (31) and that is rotatable about a holder rotation axis (C1) parallel to the table rotation axis (C2); and an engagement tool (20) that is supported by the tool holder (10) and rotates about a tool rotation axis intersecting the holder rotation axis (C1). The control device (40) has a two-axis operation mode in which the joining tool (20) is pressed against a joining site on the side surface of the workpiece (9) in a rotating state, the table (3) is rotated to move the joining tool (20) relatively along the joining site, and the tool holder (10) is rotated to face the joining tool (20) in the normal direction of the joining site. 摩擦搅拌接合装置(1)具有：工作台(3)，具有载置工件(9)的载物面(31)并且能够绕与载物面(31)交叉的工作台旋