A weld overlay system includes a rotation drive section which rotates a tube around its axis; and a welding unit which applies a weld material to the outer peripheral surface of the rotating tube, while the welding unit is advanced along an axial direction of the tube, the welding unit includes: a welding torch; and a weld material supply section which supplies the weld material, the welding torch is disposed such that a tip end of the welding torch is located at an angular position that is advanced at a predetermined angle in a direction opposite to a rotational direction of the tube, and the welding torch is inclined at a predetermined angle in the rotational direction of the tube with respect to a reference line passing through a center axis of the tube and the tip end of the welding torch, viewed from the axial direction of the tube.