This electromagnetic wave concentrator having high rigidity and flexibility is suitable for communications and is produced by molding using stress relaxation in thin-film material. An ultra-lightweight electromagnetic wave concentrator is obtained by increasing the rigidity by forming a thin-film curved body of an electromagnetic wave reflective surface having a paraboloid shape. Reinforcing grooves in the reflective surface increase rigidity. To form the reflective surface shape and the reinforcing grooves, pressure is applied to the thin-film material with a molding die, or the thin-film material is attached to the molding die by pressure while heating the thin-film material with a heating device, such as a thermostatic chamber.