A molding device is includes a mandrel that has an arc-shaped cross section; a roller that has a round-shaped cross section, is movable along a surface of the mandrel, and applies a pressing force to a material to be molded placed on the mandrel; a gripping unit that grips the material to be molded on an outside of the roller with respect to the mandrel and applies a tensile force to the material to be molded; a roller driving unit that moves the roller along the surface of the mandrel; a gripping-unit driving unit that moves the gripping unit. A control unit synchronizes a position of the roller and a position of the gripping unit with each other to control the roller driving unit and the gripping-unit driving unit so that the material to be molded is arranged in a direction perpendicular to a vertical direction of the mandrel.