PURPOSE: To provide an RF cavity resonator jointing method that sure vacuum seal performance, proper RF contact face pressure and a jointing force with high stiffness are obtained at a jointing part of an RF cavity resonator.

CONSTITUTION: Flat contact faces 3a, 3b, slightly recessed narrow grooves 4a, 4b and much recessed wide grooves 5a, 5b are formed over an entire circumference of a ridge face of cavities 2a, 2b to be jointed from the inner circumferential side. Then the contact faces 3a, 3b are butted to implement RF contact, a diaphragm 6a(6b) is fitted to the narrow groove 6a(6b) and continuous entire circumference welding 7 is applied to the entire circumference of the outer ridges to make vacuum sealing and plural tabs 8 are inserted between the wide grooves 5a, 5b on the circumference and welding 9 is applied to both end ridges to obtain jointing stiffness and a contact pressure.