In a resistance welding machine, an arm including one electrode tip, a drive unit including a linear guide for driving another electrode tip corresponding to the one electrode tip, and a welding unit including a welding transformer for passing a secondary current through a gun bracket for supporting the present resistance welding machine on a robot and/or the present resistance welding machine, can be mounted and removed individually as a unit with a common base or a rail main body including the linear guide as the reference thereof.