The present invention provides an X-ray CT apparatus capable of obtaining each tomographic image indicative of X-ray tube voltage dependent information of a subject with the optimum image quality by less reduced exposure. The X-ray CT apparatus includes device for setting a plurality of X-ray tube voltages and sets imaging conditions used in the photography using the respective X-ray tube voltages in such a manner that respective image noise of tomographic images photographed at the X-ray tube voltages become substantially identical to one another. The setting of the imaging conditions is the setting of X-ray tube currents. The X-ray tube currents are set based on geometrical characteristic amounts of the subject determined from each scout image in such a manner that the respective image noise of the tomographic images photographed at the plurality of X-ray tube voltages become substantially identical to one another.