To provide an optical fiber liquid level sensor excellent in shutoff property for gas such as water vapor, and excellent in flexibility as well as inhibiting lowering of detection sensitivity of the optical fiber caused by thermal damage.

The liquid level sensor of optical fiber comprises: a detector part (3) of prism shape; optical fibers for transmission (4) and for reception (5) connected to the detector; connector (6) for fixing the optical fibers for transmission and reception; and a case (2) of plastic resin for hermetically sealing the optical fibers and prism, wherein the connector (6) is fixed by a tube (7) and a spring (8) inserted in the case (2).