Rotating tool, joining device, and joining method

A rotating tool used in a joining device configured to perform friction stir welding of to-be-joined members, the rotating tool comprising:

• a main body including a fixation portion that is attached and fixed to the joining device and a rotating shaft that transmits rotating force from the joining device;
• a stir pin arranged in the main body to be rotatable by receiving the rotating force from the main body and be movable in an axial direction of the rotating shaft, the stir pin configured to perform friction stirring on the to-be-joined members by being inserted into the to-be-joined members;
• a shoulder formed of a body separate from the stir pin and arranged in the main body to receive no rotating force from the main body and be movable in the axial direction of the rotating shaft independently of the stir pin, the shoulder configured to press the to-be-joined members in a state where the shoulder is in contact with the to-be-joined members;
• a first elastic member configured to bias the stir pin toward a distal end side in the axial direction of the rotating shaft;
• and
• a first restriction member configured to restrict movement of the stir pin toward a based end side in the axial direction of the rotating shaft, wherein the first restriction member restricts the movement of the stir pin such that an amount of deformation occurring in the first elastic member with the movement of the stir pin does not exceed a maximum allowable amount of the first elastic member.