To provide an X-ray CT apparatus and an imaging method reducing an artifact and providing a tomogram with an improved image quality.

This apparatus is provided with an X-ray source, an X-ray detector oppositely disposed with the X-ray source via a subject positioned in a predetermined position and two-dimensionally aligned with a plurality of detecting elements, and an image reconstruction means reconstructing a tomogram of the subject in a preset predetermined surface based on projection data detected by the X-ray detector. The detecting elements constituting the X-ray detector are aligned to include a boundary between the detecting elements, which is detected in one sequential direction and has a primary differential of the projection data changing exceeding a preset threshold, in a surface different from the plane of the tomogram.