to force the fastener 2 to return to its original position the truck 39 s door is thereby closed subsequently the operator actuates the micro switch 6 by using a remote control or central control system to drive the movable rod 61 to move upward so that the limiting piece 622 of the stopping element 62 stops the second positioning face 523 of the positioning block 52 in a vertical direction the positioning block 52 is thereby limited so that it cannot rotate backward when the stopper 22 of the fastener 2 rotates backward the fastener 2 is stopped by the first positioning face 522 of the positioning block 52 and thus kept at a certain position the hook 21 of the fastener 2 further encloses the receiving space 3 the bolt 7 is thereby locked as shown in fig6 and fig7 when the locker is to be unlocked the operator actuates the micro switch 6 by using the central control system to drive the movable rod 61 to move downward so that the limiting piece 622 of the stopping element 62 withdraws from the second positioning face 523 of the positioning block 52 in a vertical direction to allow the positioning block 52 to freely rotate backward the locker is thereby unlocked then the operator can press down upon the slipping stop pattern 23 on the lower surface of the fastener 2 so that the stopper 22 of the fastener 2 pushes the first position face 522 of the positioning block 52 back and thus the hook 21 of the fastener 2 withdraws from the receiving space 3 thereby the bolt 7 inside the receiving space 3 can freely withdraw from the receiving space 3 as shown.