A curve sensor universally applicable to even a curving measurement target having a relatively small diameter is provided. A curve sensor to measure the curving of a curving measurement target comprises a light supply unit which guides light, a curve measurement unit which comprises a curved state detection unit and which measures the curved state of the measurement target by the change in the amount of light output through the curved state detection unit, a light transmission unit which transmits the light from the light supply unit to the curve measurement unit and a holding portion which holds the light supply unit and the curve measurement unit at predetermined positions on the measurement target.
