In order to provide an X-ray CT apparatus which can reconstruct a tomographic image with less unevenness in image quality at a high speed on the basis of projection data which is obtained by irradiating an object with X-rays, the X-ray CT apparatus of the invention includes an inverse projection phase width setting unit that sets an inverse projection phase width which is an angular width of projection data used for reconstruction, for each tomographic image, and a view weight calculation unit that calculates a view weight which is a weight coefficient multiplied by projection data within the inverse projection phase width and is a function of a view angle, for each position of a pixel of a tomographic image.