Data processing device, x-ray ct device, and reference correction method

In order to provide a data processing device, etc., whereby highly precise reference correction can be performed even when a subject protrudes into a reference channel in a majority of measurement views, the image processing device (data processing device) for an X-ray CT device according to the present invention calculates in advance a unit air calibration reference value which is the per-unit tube electric-current value of a reference value measured during air calibration, finds a reference value (estimated reference value) corresponding to an X-ray condition of the current imaging from the unit air calibration reference value and an output tube electric-current value for the current imaging, corrects a measurement reference value for the current imaging so that standardized reference data standardized by the estimated reference value are within an allowed error range, and removes the effect of protrusion.