An X-ray diagnostic apparatus in which the X-ray tube voltage is regulated through intermediary of the X-ray tube current. In the apparatus, a regulator is situated within a regulating circuit for the effective value of the filament current of the X-ray tube, and influences the effective value of the filament current for the purpose of correlating the actual value with the reference value which has been determined through the preset X-ray tube voltage. In the inventive X-ray diagnostic apparatus, on the one hand, the actual value of the X-ray tube voltage is compared with a reference value, and the filament current is influenced for the purpose of correlating the actual value to the reference value. Furthermore, the filament current which is required for a predetermined reference value of the X-ray tube voltage is also maintained constant preceding the beginning of an exposure so that, at the initiation of an exposure, the filament current already lies at least near to the correct value. Deviations of the X-ray tube voltage from the correct value are thereby smaller than in prior art apparatus.