Abstract: A strap tightener in which a specific releasable tensioning and clasping mechanism for a strap is incorporated to hold heavy loads under tension firmly in a given position. The strap tightener can advantageously be used to tie down cargo containers, motor vehicles and the like heavy loads to fixing structures on carrier vessels or carts. The strap tightener has a simple and economical structure with a reduced number of parts and is thus smoothly operable to attain good strap tensioning without incurring any damage of the strap and any loosening of the tensioned strap during the use.