To provide a load sensor using an optical fiber and utilizable for various purposes such as a ground anchor, and to improve sensitivity and accuracy of the load sensor using the optical fiber.

The basic constitution of this ring elastic body 10 is equipped with an elastic deformation part 13 equipped with a face 12 where the optical fiber 11 is wound around the outer periphery, and a pair of load application part 14 disposed across the elastic deformation part 13. In the ring elastic body, a hard member or a hard plate used for the ring elastic body is constituted from a material excellent for rust prevention or a material to which rust prevention processing is applied, or the outer peripheral face of the ring elastic body is coated by an elastic coating material having weather resistance or chemical resistance, or the peripheral face of an inner hole provided in the ring elastic body is coated by a material having oil resistance, to thereby provide the load sensor using the optical fiber and utilizable for various purposes.