An x-ray CT imaging apparatus emits an x-ray cone beam to an object to generate an x-ray CT image on the basis of a transmission x-ray which is transmitted through the object. An image generation part generates an image obtained by superposing an imaging object region display on a position setting image representing the object and displays the image on a display part. The image generation part changes the imaging object region display in accordance with an x-ray CT imaging mode selected by an imaging mode selection part.