1. An estimating apparatus, comprising: a memory storing a value of an exposure dose on a surface irradiated with X-rays emitted from an X-ray tube of an X-ray CT apparatus in association with irradiation conditions under which the X-rays are emitted from the X-ray tube of the X-ray CT apparatus; specifying circuitry configured to specify a region of a subject irradiated with the X-rays emitted from the X-ray tube of the X-ray CT apparatus on a human body model schematically representing the subject; deriving circuitry configured to assume the human body model to be at a position where the subject is arranged in radiography performed by the X-ray CT apparatus and derive, as a skin exposure dose, an exposure dose of the X-rays on a surface of the region specified by the specifying circuitry on the human body model based on the value corresponding to certain irradiation conditions used in the radiography, the value being acquired from the memory, and the certain irradiation conditions used in the radiography; and display control circuitry configured to display, on a display, information in which the skin exposure dose derived by the deriving circuitry is associated with the region on the human body model specified by the specifying circuitry.