A method of manufacturing a medical elongated body including an inner layer, an outer layer covering the outside of the inner layer, and a reinforcement body provided between the inner layer and the outer layer. The method includes an inner layer forming step of forming the inner layer, a reinforcement body forming step of forming the reinforcement body on an outer peripheral surface of the inner layer after the inner layer forming step, a cooling step of cooling at least a predetermined spot of the inner layer after the reinforcement body forming step, and an annealing step of annealing the reinforcement body which overlaps the predetermined spot of the inner layer cooled by the cooling step.