An FBG (Fiber Bragg Grating) sensor is equipped with a plurality of stress detection sensors made up from optical fibers in which gratings that reflect light of a specified wavelength are arrayed, and a stress direction converter that converts stresses applied from the exterior into stresses of a direction in which the gratings are arrayed, and which transmits the stresses to each of the gratings. Consequently, the stress direction converter can transmit stresses, which are applied from a body, to a plurality of gratings.