An X-ray image diagnosing apparatus has a radiating unit, a placement unit, a detecting unit, a supporting unit, a moving control unit, an obtaining unit, a calculating unit, and a frame rate control unit. The placement unit is placeable an object. The supporting unit supports the radiating unit and the detecting unit in opposing relationship across the placement unit. The moving control unit relatively moves the supporting unit and the object on a longwise direction of the placement unit so as to perform an X-ray imaging at different imaging positions along the longwise direction. The obtaining unit obtains X-ray image by performing the X-ray imaging. The calculating unit calculates blood-vessel data on the basis of the X-ray image and calculates a frame rate on the basis of the blood-vessel data. The frame rate control unit configured to change the frame rate on the X-ray imaging.