A particle beam forming device for forming either a linear or conical particle beam from a particle source in which particles are dispersed in a gas, includes: a reduced-pressure vessel in which pressure is reduced; a particle beam generating unit, which has one end arranged outside of the reduced-pressure vessel and an other end arranged inside the reduced-pressure vessel, and which captures the particle source from outside the reduced-pressure vessel and introduces the particle beam into the reduced-pressure vessel; and a particle beam evaluating unit for evaluating a spatial distribution of the particle beam inside the reduced-pressure vessel.