A spot welding device for a nuclear fuel skeleton, which is assembled by spot-welding guide tubes for control rods and a instrumentation tube for measuring a state of an inside of a nuclear reactor to a spacer grid that has a plurality of cells formed in a thickness direction of a plate-shaped frame for inserting fuel rods, has a instrumentation tube hole formed at a center, and has four guide tube holes formed symmetrically above and below the instrumentation tube hole. The device includes: a welding gun including: a body, a first holder and a second holder extending from a side of the body and having respective electrodes facing each other at ends, respectively, and a driving unit disposed on the body and adjusting a distance between the electrodes; and a robot connected to the welding gun and having a rotary joint for rotating the welding gun.