The objective is to make a charged particle beam transport system absorb a difference in emittances, caused when a beam is launched from an accelerator in a slow-extraction manner, and to realize a beam size having a small rotation dependency at an isocenter. A charged particle beam transport system (59) according to the present invention is characterized in that in a fixed transport unit (61), a phase of a phase space distribution of a charged particle beam (31) at an inlet of a rotating deflection unit (60) that rotates around an gantry rotation axle (15) of a rotating gantry coincides with a phase determined by a calculation based on an average value of a first phase advance and a second phase advance. The first phase advance is defined as a change in a phase, of the phase space distribution, that changes when the charged particle beam (31) travels from the inlet of the rotating deflection unit (60) to an isocenter (IC) in the case where a gantry angle is a gantry reference angle the second phase advance is defined as a change in a phase at a time when the gantry angle is pivoted by 90° from the gantry reference angle.
