Spot welding gun, having a support, a lower half-gun and an upper half-gun articulated one to the other by a pin, mounted in an oscillating configuration with respect to said support and propping up corresponding welding arms, and a working cylinder including a body and a stem moving with respect to the body so as to control the movement of the upper half-gun and of the lower half-gun. The support has a main plate from which extend two parallel support sides with an articulation axis around which the lower half-gun and the upper half-gun are articulated. The lower half-gun comprises two actuating forks to which the body of the working cylinder is articulated around an axis parallel to the articulation axis. The stem of the working cylinder has an end articulated to the upper half-gun around another axis parallel to said articulation axis.