An optical fiber unit enables secure grasping of an optical fiber sensor via a jig while avoiding damage to an optical fiber cable. The optical fiber unit for the optical fiber sensor includes an optical fiber cable, a shaft, and a head. The shaft includes a peripheral surface having a male thread, and a through-hole for an inserted optical fiber cable. The head is shaped in a hexagonal prism including six sides and a bottom. The shaft is connected to the bottom of the head. The optical fiber cable extends the head, and extends out of the head in a direction substantially parallel to two parallel sides of the six sides from at least one of the six sides excluding the two parallel sides.