one 39 s desire or favorite the position of the cord stoppers 27 should be relatively adjusted preventing excessive stretching of the first portion 252 of each lift cord 25 the present invention enables the user to conveniently adjust the position of the cord stoppers 27 relative to the lift cords 25 the position adjustment of the cord stoppers 27 is easy at first open each cord stopper 27 by force this can easily be achieved by an adult person because each lift cord 25 is fastened to the respective cord stopper 27 by a slip knot the cord stopper 27 can easily be moved upwards or downwards on the respective lift cord 25 after opened the second cover shell 272 from the first cover shell 271 after adjustment the first cover shell 271 and the second cover shell 272 are closed again normally the invention controls the sliding status of the lift cords 25 by means of the lift cord lock 26 if the lift cord lock 26 failed the slats 21 and the bottom rail 23 forced to fall by their gravity weight falling of the bottom rail 23 drives the lift cords 25 causing the second portions 251 of the lift cords 25 to move toward.