A fixed anode x-ray tube according to the present invention comprising: an enclosure that maintains a vacuum on the inside thereof; an anode that is provided inside the enclosure and generates X-rays due to the collision of thermions; and a cathode that is provided inside the enclosure and emits thermions toward the anode, wherein the anode has a target that receives thermions, and an anode body that is made of a material having a coefficient of thermal expansion different from that of the target and holds the target on the top surface, and the anode body is provided with a stress relaxation section that relaxes the stress due to thermal expansion at a position separated from the target.