Abstract: The safety device consists of a plate (1) with a manually drivable lever (3), the plate lying sideways to and mounted to swing on one of the side faces of the casing of the rifle, the plate (1) being provided on its rear edge with a heel (9) which in one position of the plate (1) lies above the top edge of the trigger (8) without interfering with the operation of the trigger, whereas in the other position, namely the safety position, the heel (9) lies above the top edge of the trigger (8) preventing it from being operated, thereby to serve as a safety device preventing the firearm from being involuntarily fired whilst the device is in the locked trigger (8) position.