According to one embodiment, an X-ray CT apparatus includes units. The unit calculates an arrhythmia index. The unit selects a normal mode or an arrhythmia mode based on the arrhythmia index. In the normal mode, after the elapse of a predetermined delay time from the characteristic wave, projection data is collected along with X-ray generation. Upon detecting an arrhythmia, the X-ray generation is temporarily stopped. In the arrhythmia mode, after the elapse of the predetermined delay time, projection data is collected along with X-ray generation. Upon detecting an arrhythmia, an arrhythmia scanning procedure corresponding to an arrhythmia type is temporarily executed, and projection data is collected along with the X-ray generation.
