It is an inside BOP (blowout preventer)in the drill string. It is simple in structure and easy to operate. When blowout is going to happen the thread connections of the Kelly are screwed out immediately and the back pressure valve is put into the I. D. Of drill pipe and then pumped downward to the required place. Thus the blowout accident can be prevented. The tool is consisting of landing sub and check valve assembly. The landing is thread connected with stop ring and tightened on and put into downhole with drill string. The landing sub is used as a sub above drill string before check valve is run in downhole.