To enhance energy storage efficiency, by combining a metallic internal member and a fiber reinforced plastic external member where long fiber yarns are wound in the circumferential direction as a reinforcement.

The rotator is provided with a metallic tubular internal member 11, a tubular external member 12 integrally combined to the outer circumference of the internal member 11, and upper and lower end plates 13 and 14. The external member 12 is a fiber reinforced plastic material, where long fiber yarns are wound in the circumferential direction and laminated in the radial direction as reinforcement, and the outer circumferential portion of each end plate 13, 14 is formed as a ring plate 13b, 14b of fiber-reinforced plastic material, by laminating a spiral textile in the axial direction as a reinforcement.