with the secondary piston 230 the pressure load transmitting device 250 is pushed toward the cross plate 270 therefore the cross plate 270 is deformed because the pressure load of the combustion gas is transmitted to the center of the cross plate 270 through the pressure load transmitting device 250 and the blades of the cross plate are separated from the sills 136 so that the main cylinder 210 the primary secondary pistons 220 230 and the pressure load transmitting device 250 are all pushed to thereby open the thrust termination port 132 accordingly the net thrust can be terminated because reverse thrust can be produced in the direction opposing to the normal thrust through the nozzle 120 that is when the thrust termination ports 132 are opened as described above the sum of the sectional areas of the thrust termination ports 132 becomes to be greater than the sectional area of the throat of the nozzle 120 to thereby produce the reverse thrust surpassing the thrust produced at the nozzle 120 and the lower motor not shown is separated and the pressure of the combustion chamber 112 is reduced and in some cases combustion is terminated according to the thrust termination device for the rocket motor of the present invention constructed as described above it is possible to accomplish the best performance in the flying stability and the control precision at stage separation of a missile or thrust termination of the rocket motor by the smooth.