An X-ray imaging system includes an X-ray source for emitting X-rays. A radiation source driver drives the X-ray source. An X-ray imaging apparatus has an FPD device incorporated therein, has pixels arranged for storing signal charge according to X-rays transmitted through an object, for outputting a radiation image of the object by conversion in an electrical signal. An ionization chamber device is discrete from the X-ray imaging apparatus, for detecting X-rays transmitted through the object. An interface port is provided in the radiation source driver, for connection with the ionization chamber device. There is a communication path for connection between the interface port and the X-ray imaging apparatus, and for transmitting a sync signal, namely request signal S1 and enable signal S2, for operating the FPD device in synchronism with a start of emitting the X-rays.
