PROBLEM TO BE SOLVED: To provide an X-ray CT apparatus with which an energy spectrum of X-rays applied on a subject can be obtained.SOLUTION: An X-ray CT apparatus 10 includes: a first X-ray detection part 231 detecting X-rays radiated from an X-ray tube 21 and transmitting through a subject P a second X-ray detection part 232 composed of a scintillator and a silicone photomultiplier, and outputting signals corresponding to incident X-ray energy by detecting X-rays incident from the X-ray tube 21 as photons and an energy spectrum acquisition part obtaining relation between energy and intensity of the X-ray incident to the second X-ray detection part 232 on the basis of output signals of the second X-ray detection part 232 and acquiring energy spectrum of the X-ray radiated from the X-ray tube 21 on the basis of the obtained relation.
