PROBLEM TO BE SOLVED: To provide an X-ray CT (Computed Tomography) apparatus capable of preventing lack of a data value in data compression.SOLUTION: An X-ray CT apparatus 1 related to the present embodiment includes: a rotary frame 113 which supports an X-ray tube 103 and an X-ray detector 107 while they face to each other, and can rotate around a rotation axis a data set generation part periodically generating a plurality of data sets according to the rotation of the rotary frame 113 on the basis of output from the X-ray detector 107 a difference data set generation part 135 generating a difference data set by calculating a difference between two data sets having the same phase in the data sets a determination part 137 determining presence/absence of lack of a data value caused by data compression to the difference data set by use of the data value in the difference data set and a prescribed threshold value a data compression part 139 compressing the difference data set determined that the data value does not lack and a data set storage part 141 storing the compressed difference data set.
