An X-ray CT apparatus according to the embodiments has a rotation base that includes a plurality of units, including an X-ray generator that irradiates a subject with X-rays, and an X-ray detector that detects X-rays transmitted through the subject. It also has a pathway that communicates between the X-ray detector and at least one other unit excluding the X-ray generator and the X-ray detector. It also has an air supplier that supplies air in the other units to the X-ray detector via the pathway. It also has a temperature measuring part that measures the temperature in the X-ray detector. It also has a controller that performs control of the air supplier based on the measured result from the temperature measuring part.