In a beam transport system, based on a beam temporal-variation related amount that has been calculated by a beam analyzer and that is a beam-position temporal variation amount or a beam diameter at a beam profile monitor, an optical parameter calculator calculates a start-point momentum dispersion function that is a momentum dispersion function (η, η′) of a charged particle beam at a start point in design of the beam transport system that is set on a beam trajectory of the accelerator； and calculates optical parameters using, as an initial condition, the start-point momentum dispersion function and a beginning condition at an irradiation position at the time of detecting profile data.
