An optical fiber vibration sensor includes a light source, an optical receiver, an optical dividing/coupling portion, a signal processing unit, and a fiber loop portion made of an optical fiber. A part of an optical fiber composing the fiber loop portion is installed inside a housing of a main body of the optical fiber vibration sensor as an optical fiber for delay and another part of the optical fiber composing the fiber loop portion is installed outside the housing as a vibration detecting optical fiber.