A friction stir welding device includes: a control device which causes a pin part to be inserted into members to be joined while causing a joining tool to rotate and which causes a joining head to move along a joint line via a robot main body; and an image pickup device which detects a junction deviation that is a deviation between the joining head and a direction along the joint line. Also, when a junction deviation is generated, this control device causes the joining head to move in a direction toward the joint line and thus resolves the junction deviation.