An optical transmission device capable of being coupled to an optical fiber includes a light source configured to emit a first light toward the optical fiber; a lens configured to converge the first light to an end of the optical fiber; a light reflector configured to reflect a first reflected light as a second reflected light, a part of the first light being reflected as the first reflected light by the lens or the optical fiber; a first light receiver configured to receive the second reflected light; a detector configured to detect a failure based on a difference value between a first value corresponding to an amount of the second reflected light and a reference value being indicative of an amount of the second reflected light, the second reflected light being detected when the first light is normally emitted and is normally transmitted to and through the optical fiber.