an x - ray computed tomography apparatus includes an x - ray tube configured to emit x - rays , an x - ray detector configured to detect x - rays passing through a subject in order to acquire projection data , a processor configured to reconstruct tomographic image data on the basis of the projection data , and an interlock unit configured to monitor generation of an arc in the x - ray tube . when an arc in the x - ray tube is detected , the interlock unit stops emitting x - ray emission from the x - ray tube . when a predetermined period of time elapse from the stop of x - ray emission , the interlock unit restarts x - ray emission from the x - ray tube .