1. An X-ray photographing apparatus comprising: an X-ray generator configured to generate an X-ray; an X-ray detector configured to detect the X-ray that is transmitted through an object; and a panel that is provided between the X-ray generator and the X-ray detector and configured to contact the object, wherein a radiation angle of the X-ray generated by the X-ray generator with respect to the object is configured to change with a distance between a center axis of the X-ray generator and a center axis of the X-ray detector maintained to be constant, and the X-ray generator comprises: a plurality of electron emission devices configured to emit electrons; and an anode electrode configured to generate the X-ray by using the emitted electrons, wherein the radiation angle differs according to a thickness of the anode electrode.