The present invention is directed to realize an X-ray CT apparatus and a scan control method of performing contrast imaging by a helical shuttle scan with a smaller exposure amount. An X-ray CT apparatus for performing contrast imaging by repeating a reciprocating helical scan on a region in a subject repeats the helical shuttle scan (solid-line arrow) including, in shuttle (broken-line arrow) of a helical shuttle scan using an X-ray of a first X-ray dose, a helical scan using an X-ray of a second X-ray dose higher than the first X-ray dose. The start timing of the helical scan using the X-ray of the second X-ray dose is determined on the basis of a change in the CT number of a region of interest of an image captured by a helical scan using the X-ray of the first X-ray dose.