Safety device is a safety gear when the crushing chamber of jaw crusher enters non-breaking material (eg. Iron, etc), in order to make the main components of the machine from being damaged. The most common is to use the latter thrust plate as the safety device of the crusher. The latter thrust plate is made of ordinary cast iron in general, and in which opens a tank or a number of holes in order to reduce the strength of its cross section; or by a combination thrust plate. When the crushing chamber falls in non-breaking material, the machine excesses the normal load, the latter thrust plate is damged and makes the crusher stop working, so that the main components of the crusher machine are not damaged.