[en] The present invention provides a neutral particle injection device useful for additionally heating generated plasmas in a thermonuclear device utilizing magnetic fields to confine plasmas. Namely, a cryopump for evacuating channels of charged particle beams is made of a superconductive material. A magnetic shield utilizing a Meissner effect is also provided by using the superconductive material. Then, since the cryopump and the vacuum vessel also having the effect of the magnetic shield at high shielding rare are provided, the structure is simplified as a whole and reduced in the size, and the installation space can be saved. Since the Meissner effect at a cryogenic temperature is utilized as a magnetic shield, magnetic fields of several kilogauss can be reduced to 1/100,000. Since the thickness of the material to be used both for the magnetic shield and the cryopump can be reduced to about several millimeters, the weight of the neutral particle injection device can be reduced. (I.S.)