A curvature sensor includes a light source, a flexible light guide including cores, and FBG sensors that are provided in the cores and constitute FBG sensor groups at predetermined positions at predetermined positions along longitudinal axes of the cores. The curvature sensor includes a detector that detects an optical spectrum of light from the FBG sensors, and a processor that obtains a bend of the light guide. FBG sensors provided in a core include a first FBG sensor and a second FBG sensor next to it. The first and second FBG sensors include gratings having first and second pitches. The first pitch is shorter than the second pitch and is closer to the second pitch than other pitches of gratings of all FBG sensors that are provided in the core and include gratings having pitches shorter than the second pitch.
