A computed tomographic mammography system is provided with, as an X-ray tube 1A, a transmission type X-ray tube including a target 2 which includes a target layer 2a that generates X-ray upon irradiation of an electron beam and a supporting substrate 2b through which the X-ray generated upon irradiation of the electron beam to the target layer 2a passes, an electron emission source 3 for emitting an electron beam toward the target layer 2a.
