Abstract: One end of the mobile jaw of a jaw crusher is supported on the crusher frame by an eccentric shaft and a connecting rod supports the other mobile jaw end on a crossbeam pivotally mounted on the frame. The crossbeam has a rear extension accessible from outside the frame and a control wedge is positioned on a bracket affixed to the frame between the bracket and the crossbeam extension. A safety system acts on the crossbeam extension for preventing pivoting thereof when the force applied by the mobile jaw to the crossbeam remains below a predetermined value, the safety system pressing the crossbeam extension against the control wedge.