PURPOSE: To facilitate the adjustment of the axis of a neutral particle analyzer by forming a refraction path for laser light in such a manner as to cause an axis of the laser light to coincide with the incidence axis of neutral particles and causing another optical axis of the laser light to coincide with the central index of a light-receiving plate installed in the vacuum case.

CONSTITUTION: Neutral particles emitted from a neutral particle source 1 become incident upon a stripping cell 4 installed in a vacuum case 3 and are converted into charged particles. The thus produced charged particles are then analyzed by a microchannel detector 7 after being passed through deflecting electromagnets 5 and 6. In the peripheral area of the vacuum case 3, a refraction path 14 is formed in which laser light discharged from a laser producer 10 is refracted by mirrors 16 and 17 to introduce the axis 9 of the laser light to the incidence axis 2 of the neutral particles. At the same time, the position of the axis 20 of the laser light is controlled by a light- receiving plate 19 and the positions of the laser light axis 9 and the neutral particle incidence axis 2 are controlled by a light-receiving plate 21. Consequently, it is possible to install the laser producer 10 in any position inside a wider area, thereby facilitating the adjustment of the axis of the neutral particle analyzer.