A curved shape sensor to detect a curved shape of a measured object includes a light source to emit detection light, an optical fiber to guide the detection light, a detection part provided at a portion of the optical fiber, a rotation suppressing member fixed to the optical fiber, and a light detection unit to detect the detection light traveling through the optical fiber. The measured object includes a tubular member having flexibility so as to be curved, and an incorporation member located inside the tubular member. The detection part changes characteristics of the detection light in accordance with a change in a curvature of the optical fiber. The rotation suppressing member is located within a space defined by the tubular and incorporation members with being in contact with them, so as to suppress rotation of the optical fiber.