To provide a friction rotary welding machine capable of welding a joint and a tube stock easily at a low cost.

The machine is equipped with a joint holding member that has a tubular shape whose inner diameter is about the same as the outer diameter of a joint, that is divided into plural divisions which can be freely assembled in the cross section of the axial direction, and that has gears around; equipped with a joint supporting part having a driving force transmitting means, which rotation-freely supports this joint holding member around the tubular axis of the held joint, which meshes with the gears of the joint holding member when the joint holding member is supported, and which thereby transmits the rotary driving force of a motor to the joint holding member; and equipped with a tube stock supporting means that supports the tube stock in the manner that the tubular axis of the tube stock is aligned with that of the joint held by the joint supporting part, that moves relative to and in the direction of the joint supporting part, and that retains the end of the held tube stock in a manner inserted into the socket of the joint.