A treatment planning system for performing treatment planning of a charged particle beam treatment includes a calculation unit that calculates a dose distribution and an irradiation time required for the irradiation in a case where an irradiation target body is irradiated with a charged particle beam, corresponding to a plurality of predetermined cut-off dose values, and an output unit that outputs each of the cut-off values, data based on the dose distribution corresponding to each of the cut-off dose values, and the irradiation time corresponding to each of the cut-off dose values, to a display unit. The calculation unit cuts off an irradiation location having a dose which is equal to or smaller than the cut-off dose value, from doses required in respective irradiation locations of the irradiation target body, and thereafter, sets a current value of the charged particle beam when the dose distribution is calculated.
