An X-ray CT apparatus, which is capable of quickly acquiring information for determining whether further CT imaging is required, is provided. The X-ray CT apparatus according to the embodiment comprises a reconstruction processor, a setting unit, and a controller. The reconstruction processor carries out first reconstruction processing to be carried out at a first image thickness based on detection data to be sequentially acquired by X-ray scanning of the desired site of a subject, and second reconstruction processing to be carried out at a second image thickness based on all detection data acquired by the X-ray scanning. The setting unit sets the first image thickness based on the second image thickness set in advance. The controller allows the reconstruction processor to initiate the first reconstruction processing in parallel with the X-ray scanning at the set first image thickness and initiate the second reconstruction processing at the second image thickness once the first reconstruction processing is completed.