Abstract: A protection device is provided for a machine which works sheet shaped material to stop the displacement of the machine when the protection device encounters an obstacle. The machine includes clamps which are displaced by the machine and which hold the material. The protection device includes two blades arranged parallel to each other and disposed on the machine in a loop shape surrounding each clamp. The two blades form a pair of normally open contacts of which at least the outer blade is flexible and resiliently deformable to allow the blades to be brought into contact with each other and close the contacts when the outer blade encounters the obstacle. A stop device is coupled to the normally open contacts to stop the displacement of the machine when the contacts are closed.