Abstract: A spring pre-tensioning device for a roll blind is provided. The pre-tensioning device includes a rotation shaft including a threaded part, with a restraining protrusion provided on the threaded part, and a locking groove. The pre-tensioning device also includes a restraining nut engaged with the threaded part of the rotation shaft, and disposed on the restraining protrusion, so as to prevent the restraining nut from moving further forward; a restraining body provided with a shaft insertion hole therein, and provided with a locking protrusion and a locking clip and a spring. The restraining body is fitted over the outer circumferential surface of the rotation shaft and is fixedly connected to the spring is rotated to apply a predetermined pretension value to the spring, and is engaged with the restraining nut that is prevented from forward rotation, thereby restraining pretension of the spring.