A radiation CT apparatus includes a rotation unit configured to rotate about a rotation axis, a radiation generation unit and a radiation detector which are fixed on either side of the rotation axis in the rotation unit, and a gantry cover containing the radiation generation unit and the radiation detector and including a breast insert portion configured to insert a breast of an object. An opening portion that can be opened and closed is placed on the gantry cover of the radiation CT apparatus. The radiation generation unit and the radiation detector are stopped to form a space that allows a user to access the breast insert portion from the opening portion.
