PURPOSE: To provide a treatment system having a simple, small constitution, using a first controlling means for controlling energy outgoing from a synchrotron so as to apply beams effective for a treatment and a second controlling means for controlling excitation quantities of electromagnets in a beam transporting system.

CONSTITUTION: A beam treatment apparatus comprises an incident part 1 for ionizing particles, such as neutrons, and accelerating the ionized particles to form a particle beam; a synchrotron 2 for accelerating the formed particle beam; a beam transporting system 3 for inducing the particle beam outgoing from the synchrotron 2 to a desired part of a patient; and a treatment system 4 for applying the particle beam to the desired part of the patient, such as tumors. The energy of a beam outgoing from the synchrotron 2, which energy changes with time, is once accelerated to a maximum level and then, the energy is lowered in a controlled manner by a controlling apparatus 25 so that a beam having energy effective for a treatment can be applied. In a magnetic field corresponding to the energy of the outgoing beam, which energy changes with time, excitation quantities of deflecting magnets 31 in the beam transporting system 3 are controlled by a controlling apparatus 32.