A separation preventing device that prevents separation of a fluid pipe in a pipe axis direction, includes a main body externally fitted to an outer peripheral surface of the fluid pipe and has a recess portion facing the outer peripheral surface; a locking member housed in the recess portion in a tiltable manner and is able to bite into the outer peripheral surface of the fluid pipe; and pressing units that are provided in the main body and press the locking member, wherein the locking member has a plurality of wedge portions in a front-back direction of a pipe axis of the fluid pipe, and is equipped with a projection portion that regulates biting of a front wedge portion of the plurality of wedge portions into the fluid pipe, when the fluid pipe moves to a separation side in the pipe axis direction.