In an X ray imaging system, a rotational support device (21) supports an X ray source (11) in a rotatable manner, to adjust an orientation angle (α) thereof. An angle detector (22) is disposed on the X ray source removably, for detecting the orientation angle. A shift determiner (33a) operates when the X ray source is moved pivotally, and determines a shift amount (ΔH) for an FPD device (12) to a position opposed to the X ray source according to the orientation angle from the angle detector and a distance (SID) between the X ray source and the FPD device. A pseudo signal generator (34) generates a pseudo signal (Vout) of a level irrespective of the shift amount by correcting a detection signal from a shift detector (31) according to the shift amount from the shift determiner, and supplies a second moving device (13) with the pseudo signal. Movement of the FPD device is controlled according to the shift amount.
