An object of the invention aims is to provide a radiation treatment simulation apparatus (10) that improves the simulation precision of a therapeutic dose in radiation treatment. The radiation treatment simulation apparatus (10) includes a calculating unit (5) that calculates the therapeutic dose distribution of radiation with which a patient is to be irradiated in the radiation treatment, and an information storage unit (3) that stores information on an administered medicine that is a sensitizer or a protective agent to be administered to a patient in the case of the radiation treatment, and a calculating unit (5) calculates the therapeutic dose distribution on the basis of the information on the administered medicine stored in the information storage unit (3).
