a return preventing device preventing return of an object driven when a vehicle suddenly decelerates includes : a gear receiving drive force of a drive device , which drives the object , so as to rotate in a first direction , and transmitting the drive force to the object so as to drive the object ; a rotation - preventing pawl disposed so as to be meshable with the gear , and preventing rotation of the gear in a second direction opposite the first direction in a state in which the rotation - preventing pawl and the gear are meshed ; and an elastic member for making the rotation - preventing pawl mesh with the gear substantially synchronously with rotation of the gear in the second direction . accordingly , the rotation - preventing pawl reliably meshes with the gear substantially synchronously with rotation of the gear in the second direction .