An X-ray generating tube comprising: an insulating tube having a first open end and a second open end; a cathode including an electron emission source and arranged to close the first open end of the insulating tube; an anode including a target that generates an X-ray upon collision with an electron from the electron emission source and arranged to close the second open end of the insulating tube; and a tubular electrical conductive member extending from the anode in an inner space of the insulating tube, wherein the insulating tube includes a tubular rib at a position spaced apart from the first open end and spaced apart from the second open end, the tubular rib is arranged in a radial direction when viewed from an end of the tubular electrical conductive member on a side of the cathode, the end of the tubular electrical conductive member on the side of the cathode is positioned between a first virtual plane including an end face of the tubular rib on the side of the cathode and a second virtual plane including an end face of the tubular rib on a side of the anode; an end face of the tubular electrical conductive member on the side of the cathode is spaced apart from the first virtual plane; the end face of the tubular electrical conductive member on the side of the cathode is spaced apart from the second virtual plane; a thickness of a portion of the insulating tube where the tubular rib is arranged is larger than a thickness of a remaining portion of the insulating tube where the tubular rib is not arranged such that the tubular rib increases a strength of the insulating tube, and characterized in that the insulating tube and the tubular rib are made of an insulator. an insulating tube having a first open end and a second open end; a cathode including an electron emission source and arranged to close the first open end of the insulating tube; an anode including a target that generates an X-ray upon collision with an electron from the electron emission source and arranged to close the second open end of the insulating tube; and a tubular electrical conductive member extending from the anode in an inner space of the insulating tube, wherein the insulating tube includes a tubular rib at a position spaced apart from the first open end and spaced apart from the second open end, the tubular rib is arranged in a radial direction when viewed from an end of the tubular electrical conductive member on a side of the cathode, the end of the tubular electrical conductive member on the side of the cathode is positioned between a first virtual plane including an end face of the tubular rib on the side of the cathode and a second virtual plane including an end face of the tubular rib on a side of the anode; an end face of the tubular electrical conductive member on the side of the cathode is spaced apart from the first virtual plane; the end face of the tubular electrical conductive member on the side of the cathode is spaced apart from the second virtual plane; a thickness of a portion of the insulating tube where the tubular rib is arranged is larger than a thickness of a remaining portion of the insulating tube where the tubular rib is not arranged such that the tubular rib increases a strength of the insulating tube, and characterized in that the insulating tube and the tubular rib are made of an insulator.