PROBLEM TO BE SOLVED: To provide an X-ray CT apparatus capable of preventing lack of a data value in data compression.SOLUTION: An X-ray CT apparatus 1 includes: a rotary frame 113 which supports an X-ray tube 103 and an X-ray detector 107 so as to face each other and is rotatable around a rotation axis a data set generation part for periodically generating a plurality of data sets according to rotation of the rotary frame 113 on the basis of an output from the X-ray detector 107 a difference data set generation part 135 for 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 for determining whether the difference data set lacks the data value due to data compression by using the data value in the difference data set and a prescribed threshold a data compression part 139 for compressing the difference data set determined not to lack the data value and a data set storage part 141 for storing the compressed difference data set.SELECTED DRAWING: Figure 1
