To terminate a high-energy particle beam by efficiently decelerating it without generating radiation.

Plasma of an encapsulated gas is generated with the incident high-energy particle beam 3 by encapsulating the gas in a waveguide 1 of a linear decelerator, the generated plasma is resonated and vibrated in the waveguide, and the plasma vibration energy is supplied to a load device 9 by taking it out to the outside by electrodes 5a-7a as electrical energy.