The idea behind the system used for this device is the one to fit out the moving part of the press brake with a protection zone. This is a volume of suitable and special dimensions generated by the laser and placed under the upper tool vertex at a higher distance than that the machine requires to stop. So the protection zone, that moves together with the mobile part because integral with it, advances the race of this one towards the fixed part. An obstacle (for example the operator fingers) when entering the protection zone, is detected immediately causing consequently the interruption of the mobile part motion. As the detection takes place at a higher distance than that the machine requires to stop, the crushing possibility between the two tools may be excluded.