The molding method of the present invention configures: a mandrel 2 being a mold for molding the material of a fiber-reinforced plastic 1 and having multiple pieces 21 to 24 adjacent to one another in a longitudinal direction D; and an angle material 3 formed of a material having a linear expansion coefficient approximate to the linear expansion coefficient of the fiber-reinforced plastic, and aligning the pieces 21 to 24 along the longitudinal direction D. The method includes: a mandrel disposing step S2 of disposing the pieces 21 to 24 with gaps G1 to G3 between one another; an angle material disposing step S3 of disposing the angle material 3 on the pieces 21 to 24; and a heating to cure and molding step S5 of molding the fiber-reinforced plastic by heating the material of the fiber-reinforced plastic while aligning the pieces 21 to 24 by the angle material 3.