A medical X-ray CT photography apparatus, comprising: a support that supports an X-ray generator and an X-ray detector while the X-ray generator and the X-ray detector are opposed to each other with a subject interposed therebetween, wherein the X-ray generator is configured to emit an X-ray beam and the X-ray detector is configured to output an electric signal according to an intensity of a detected X-ray; a support retention part that is configured to support a turning shaft provided in said support; a turning part that is configured to turn said support about said turning shaft with respect to said support retention part; a subject chair on which said subject sits; a chair moving mechanism that is configured to linearly move said subject chair relative to said support in a direction orthogonal to said turning shaft and a front-back direction of said subject; and a control part that is configured to perform panoramic X-ray photography in which a dental arch of said subject is irradiated with said X-ray such that said dental arch is scanned with said X-ray from the right to the left or from the left to the right by controlling said chair moving mechanism and said turning part in a conjunction way, wherein said control part is configured to control said chair moving mechanism and said turning part such that said subject chair moves relatively backward with respect to said support when viewed from the subject who sits on the subject chair while said X-ray detector moves from one side to the front of a head of said subject, and said subject chair moves relatively frontward with respect to said support while said X-ray detector moves from the front of said head to the other side. a support that supports an X-ray generator and an X-ray detector while the X-ray generator and the X-ray detector are opposed to each other with a subject interposed therebetween, wherein the X-ray generator is configured to emit an X-ray beam and the X-ray detector is configured to output an electric signal according to an intensity of a detected X-ray; a support retention part that is configured to support a turning shaft provided in said support; a turning part that is configured to turn said support about said turning shaft with respect to said support retention part; a subject chair on which said subject sits; a chair moving mechanism that is configured to linearly move said subject chair relative to said support in a direction orthogonal to said turning shaft and a front-back direction of said subject; and a control part that is configured to perform panoramic X-ray photography in which a dental arch of said subject is irradiated with said X-ray such that said dental arch is scanned with said X-ray from the right to the left or from the left to the right by controlling said chair moving mechanism and said turning part in a conjunction way, wherein said control part is configured to control said chair moving mechanism and said turning part such that said subject chair moves relatively backward with respect to said support when viewed from the subject who sits on the subject chair while said X-ray detector moves from one side to the front of a head of said subject, and said subject chair moves relatively frontward with respect to said support while said X-ray detector moves from the front of said head to the other side.