An optical fiber length adjuster includes an entrance 15 and an exit 16 for an optical fiber 9, and a holding portion 14 to hold the optical fiber 9 so that the optical fiber 9 is deformed. The holding portion 14 is configured to decrease the length of the optical fiber 9 that is held, when tensile force applied to the optical fiber 9 is increased, and increase the length of the optical fiber 9 that is held, when the tensile force applied to the optical fiber 9 is decreased.
