There is disclosed a radiation treatment planning system for preparing treatment planning information for carrying out radiation treatment. The apparatus includes an input unit with which an operator inputs a prescription dose and an irradiation angle an arithmetic unit which prepares the treatment planning information by determining irradiation conditions in such a manner as to bring a dose distribution calculated based on the result of the input from the input unit closer to the prescription dose, and a display unit which displays the treatment planning information. The arithmetic unit sets, per point for radiation irradiation, an index representing the degree of demand for irradiation amount suppression, the degree of demand determined by the radiation irradiation point, and the arithmetic unit further determines the irradiation conditions using the index.
