A motor-driven resistance spot welding machine includes: a drive rod having an electrode tip on an end thereof and making a linear motion; a linear guide for guiding the linear motion of the drive rod, the linear guide including a bearing; and a reduction gear being supported by a gun arm or a gun bracket. The machine also linearly drives the drive rod in an electrode force direction by transmitting an output torque of an electric motor to the reduction gear. In the machine, a rear portion of the drive rod is connected to a swing lever through a link, the swing lever being secured either to an output shaft of the reduction gear or to a main body of the reduction gear, whereby an arcuate motion is transmitted to the swing lever by an output of the electric motor, and is then converted into a linear motion of the drive rod by the link to thereby drive the drive rod so as to apply electrode force. As a result of this construction, the reduction gear is sealed, so that the reduction gear is free from welding splashes. Such problems as the large moment of inertia (GD.sup.2) and the restricted strokes of the ball-bearing leadscrew and the nut can be overcome. Further, gun parts are grouped by function. That is, the functions are unitized into a drive unit for generating electrode force, and a welding unit including the electrode tips, the gun arm, the welding transformer, and the like, so that parts are unitized into common parts so as to be standardized. Further, a new bracket which can be used irrespective of the posture of the gun attached to the robot can be realized.