Provided is an X-ray generating tube including an electron gun, which includes a grid electrode secured to a support member. In the X-ray generating tube, thermal stress generated at a joining portion between the support member and the grid electrode is reduced, to thereby maintain a position of an electron beam on a target irradiated with the electron beam accurately for a long time. A grid electrode and a support member are secured to each other via a buffer member, which has an elastic coefficient that is lower than elastic coefficients of the grid electrode and the support member, and which is joined to the grid electrode and the support member through a first joining portion on the grid electrode side and a second joining portion on the support member side, respectively.

Provided is an X-ray generating tube including an electron gun, which includes a grid electrode secured to a support member. In the X-ray generating tube, thermal stress generated at a joining portion between the support member and the grid electrode is reduced, to thereby maintain a position of an electron beam on a target irradiated with the electron beam accurately for a long time. A grid electrode and a support member are secured to each other via a buffer member, which has an elastic coefficient that is lower than elastic coefficients of the grid electrode and the support member, and which is joined to the grid electrode and the support member through a first joining portion on the grid electrode side and a second joining portion on the support member side, respectively.