A liquid detector (1) includes a plurality of optical fibers (11A, 11B, 11C) provided with bent portions, light emitting elements (12A, 12B, 12C) which are respectively provided in the optical fibers (11A, 11B, 11C) and input light according to electrical signals input from the outside to one end of the optical fibers (11A, 11B, 11C), and light receiving elements (13A, 13B, 13C) which are respectively provided in the optical fibers (11A, 11B, 11C) and output electrical signals according to light emitted from the other end of the optical fibers (11A, 11B, 11 C) to the outside. The bend radiuses (Ra, Rb, Rc) of the bent portions of the optical fibers (11A, 11B, 11C) are set in accordance with the refractive indexes of associated liquids to be detected.