To provide a force sensor and a force measuring system that can improve stability and sensitivity as a sensor by solving the problem of a conventional force sensor utilizing the flexural loss of an optical fiber while utilizing the original advantages of the optical fiber.

Rounded parts 22 and 24 being subjected to flexural deformation are provided at an elastic body beam 10, a radius of curvature is increased by applying a load in the rounded part 22, and the radius of curvature is decreased in the rounded part 24. Separated optical fibers 11 and 12 are applied to the rounded parts 22 and 24, respectively, and the change in the pure increase and decrease of the quantity of transmission light in the optical fibers 11 and 12 in a case where the load is applied to the elastic body beam 10 is detected, thus detecting the great change in the quantity of light and increasing the sensitivity of a sensor. Also, the flexural deformation with superior repeatability of the elastic body beam 10 can be transferred to the optical fibers 11 and 12, thus improving repeatability and durability as the sensor.