To provide a device for destructing a high-altitude high-speed missile such as a huge meteorite by generating small nuclear explosion by small fissile substance amount.

By opening/closing through the remote control of a valve 268 attached in the middle of a propulsion gas pipe 69, propulsion gas 65 is emitted from a nozzle 71 fixed to the outer face of each of a storage container 3 and an auxiliary tank 60 to the external world to wait a high-speed missile in its advancing direction. By injecting an excessive moderator nuclear fuel solution 61 into the air gap of excessively small solid moderator-mixed gadolinium addition nuclear fuel rod lattice 50 with a pump 63, a moderator ratio is optimized and kinf is maximized. When the kinf becomes maximum, neutron is generated to cause nuclear explosion.