To provide an inexpensive X-ray CT apparatus which enables high-speed and high spatial-resolution imaging.

At least a part of an X-ray detector is configured by placing the followings in a channel (CH) direction in a prescribed repeated pattern: a first detection element group 241 having a plurality of X-ray detection elements 24a which have a first width in the z direction and are placed in the z direction; and a second detection element group 242 having a plurality of X-ray detection elements 24b which have a second width, that is greater than the first width, in the z direction and are placed in the z direction. Projection data obtained by the second detection element group 242 is employed for image reconstruction by interpolating the projection data in the z direction by means of weighted addition processing.

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