A charged particle beam transport system is characterized in that in a fixed transport unit, a phase of a phase space distribution of a charged particle beam at an inlet of a rotating deflection unit that rotates around an gantry rotation axle 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 travels from the inlet of the rotating deflection unit to an isocenter 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.