A forming system that forms a metal pipe from a cylindrical metal pipe material having a welded portion in which end portions of a plate material are welded to each other, the forming system comprising: a forming apparatus which includes a set of dies, and a heating and expanding part which heats the metal pipe material disposed between the set of dies and supplies a gas into the metal pipe material to expand the metal pipe material; characterized in that the forming system further comprises: a supply device which rotates the metal pipe material around a central axis of the metal pipe material and supplies the metal pipe material to the forming apparatus; a position detection unit which detects a direction in which the welded portion is located with respect to a center of the metal pipe material in a case of being viewed from an extension direction, before the metal pipe material is supplied to the forming apparatus by the supply device; and a control device which includes a storage unit and a control unit and controls an operation of the supply device, wherein in a case where a position at which a distance from the center of the metal pipe material is the longest, on a surface of any one of the dies of the set of dies, in a space which is formed by the cavity of the set of dies, in a case of being viewed from the extension direction of the metal pipe material in a state where the metal pipe material is disposed between the set of dies, is set to be a longest position, the storage unit stores information on the longest position, and the control unit controls, based on the information on the longest position stored in the storage unit, a supply of the metal pipe material to the forming apparatus by the supply device such that the welded portion is not located on a straight line connecting the longest position and the center of the metal pipe material. a supply device which rotates the metal pipe material around a central axis of the metal pipe material and supplies the metal pipe material to the forming apparatus; a position detection unit which detects a direction in which the welded portion is located with respect to a center of the metal pipe material in a case of being viewed from an extension direction, before the metal pipe material is supplied to the forming apparatus by the supply device; and a control device which includes a storage unit and a control unit and controls an operation of the supply device, wherein in a case where a position at which a distance from the center of the metal pipe material is the longest, on a surface of any one of the dies of the set of dies, in a space which is formed by the cavity of the set of dies, in a case of being viewed from the extension direction of the metal pipe material in a state where the metal pipe material is disposed between the set of dies, is set to be a longest position, the storage unit stores information on the longest position, and the control unit controls, based on the information on the longest position stored in the storage unit, a supply of the metal pipe material to the forming apparatus by the supply device such that the welded portion is not located on a straight line connecting the longest position and the center of the metal pipe material.