Provided is an X-ray generating apparatus, which includes: an X-ray generating tube configured to emit X-rays through a first window； an outer case configured to contain the X-ray generating tube and provided with a second window transmitting the X-rays at a position facing the first window； an insulating fluid with which an unoccupied space of the outer case is filled； an insulating member located between the first window and the second window and provided with an opening in an irradiation area of the X-ray through the first window； and an insulating third window removably fit into the opening of the insulating member, wherein a linear expansion coefficient of the third window is greater than a linear expansion coefficient of the insulating member, and the third window and the first window face each other via a gap through which the insulating fluid is flowable.
