A unit for X-ray CT imaging to be set in a panorama X-ray imaging apparatus having a cassette holder has a digital sensor cassette for CT imaging to be set in the cassette holder, includes a two-dimensional X-ray detector for acquiring X-ray projection data for CT imaging of an object, and a controller for controlling a timing of X-ray CT imaging, a radiation field of X-ray beam generated by the X-ray detector, and the rotary device. Alternatively, the unit has the digital sensor cassette for X-ray CT imaging, an image reconstructor which calculates to convert the X-ray projection data obtained with the two-dimensional X-ray detector to a distribution of X-ray absorption coefficients of the object and creates tomographic image data of sections of the object, and an image processor which sends and receives signals for X-ray CT imaging between the X-ray detector and the image reconstructor when the digital sensor cassette for CT imaging is set in the cassette holder.