1. An X-ray diagnostic system comprising: an X-ray source irradiating an X-ray; an X-ray detector detecting the X-ray; a support apparatus configured to support both the X-ray source and the X-ray detector so that both the X-ray source and the X-ray detector are opposed to each other with a space left therebetween, a tabletop on which an object to be examined is laid being located in the space, the object being subjected to injection of an X-ray contrast agent when the object is examined; a fluoroscopic scan unit configured to relatively move one of both the tabletop and the support apparatus to the other and to perform a fluoroscopic scan along a direction predetermined with respect to the object with the one of both the tabletop and the support apparatus relatively moved to the other, the X-ray contrast agent flowing substantially along the direction, thereby a fluoroscopic image of the object being provided along the direction; an imaging parameter setting unit configured to set, at every region to be examined of the object, imaging parameters required for an imaging scan on the basis of the fluoroscopic image, the regions being at least continuous without a gap along the direction determined with respect to the object; and an imaging scan unit configured to relatively move the one of both the tabletop and the support apparatus to the other and, with the one of both the tabletop and the support apparatus relatively moved to the other, perform the imaging scan on the object on the imaging parameters set by the imaging parameter setting unit.