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