Particle beam therapy system

A particle beam therapy system comprising:

• an accelerator that accelerates a charged particle beam;
• an irradiation apparatus that has a beam scanning apparatus for performing scanning with the charged particle beam and a first duct in which a beam outlet window is provided at a more downstream position than the beam scanning apparatus, and that irradiates the charged particle beam onto an irradiation subject through the inside of the first duct;
• a beam transport apparatus that has a second duct and transports, through the inside of the second duct, the charged particle beam exciting from the accelerator to the irradiation apparatus;
• and
• a rotating gantry in which part of the beam transport apparatus and the irradiation apparatus are mounted, wherein the first duct is provided with a duct extension/contraction means that enables the beam outlet window to travel in the axis direction of the charged particle beam;
• and in the case where the charged particle beam is irradiated onto the irradiation subject, the duct extension/contraction means is extended, and in the case where the rotating gantry is rotated, the duct extension/contraction means is contracted.