An X-ray CT apparatus is provided which can easily decide on a reconstruction method based on imaging conditions. The X-ray CT apparatus comprises an irradiation unit irradiating a subject with X-rays, a detector configured to detect X-rays transmitted through the subject, and a rotator rotating irradiation unit and detector around the subject, and which generates an image by receiving biological signals of the subject to perform synchronous imaging. A memory stores a threshold value. Processing circuitry calculates, based on imaging conditions related to the synchronous imaging, a detection data amount in which detection data amount detected by the detector is represented by a number of rotations of the rotator, decides, based on the detection data amount and the threshold value, on a reconstruction process for implementation on the detection data, and implements reconstruction processes based on the detection data to generate the image.
