1. An X-ray CT apparatus comprising: an X-ray source configured to generate X-rays towards a subject; a rotation mechanism configured to rotate the X-ray source around a rotational axis; an X-ray detector having a plurality of detection elements arranged in a first direction roughly parallel to the rotational axis and in a second direction which is different from the first direction and configured to detect X-rays emitted from the X-ray source; a blocking member located between the X-ray source and the X-ray detector and configured to block X-rays; a reconstruction unit configured to reconstruct an image of the subject in accordance with the data detected by the X-ray detector; and the blocking member comprising an aperture including a first section and a second section, the second section located in the first direction in relation to the first section and staggered in relation to the first section in the second direction.