an apparatus for closing a succession of partly disengaged slide fastener coupling element chains with sliders mounted respectively thereon includes an element - engaging block assembly having a guide channel for constrictingly receiving a disengaged portion of each coupling element chain to close the same . the assembly includes a movable element - engaging block reciprocably movable toward and away from a stationary element - engaging block to selectively define therebetween the guide channel in timed relation to detection by a sensor of an element - free space between the successive chains and the slider .