According to the invention, an X-ray CT apparatus includes: an annular rotator including: an X-ray tube; an X-ray detector disposed oppositely to the X-ray tube; a radiator disposed in the vicinity of the X-ray tube and dissipating heat from the X-ray tube; an air outlet provided in the vicinity of the radiator; and an air inlet provided at a position oppositely to the air outlet, a gantry cover covering peripheral of the annular rotator and having an upper air vent and a plurality of lower air vents; a plurality of fans discharging to the outside air exist in a gap between the gantry cover and the annular rotator from the air outlet; and a baffle plate provided in the gap in the vicinity of the lower air vents and controlling an air flow passing through internal space of the annular rotator and an airflow passing through the gap.