For the purpose of providing a transportable linear accelerator system which can restrain entering of losing ion beams deviated from a trajectory therefor, to thereby efficiently achieve reduction in radioactivity at low cost, and a transportable neutron source equipped therewith, a transportable linear accelerator system is configured to be provided with a beam chopper just before an inlet of a post-accelerator, thereby to cut off, from the proton beams pre-accelerated by a pre-accelerator, uncontrolled proton beams, and thus to radiate only the controlled proton beams to the post-accelerator, so that the proton beams are prevented from hitting an acceleration electrode, etc. of the post accelerator.