PURPOSE: To provide an applying force control device of a spot welding gun which is driven by an electric motor so that the applying force control of the spot welding gun may be obtained by the closed loop control at low cost and the applying force suitable for the welding may correctly be obtained.

CONSTITUTION: In a spot welding gun which is driven by an electric motor M, a spring 12 is stretched between a spring holding member 8 at the fore part of a reed screw 7 which is reciprocated interlockingly with the rotation of the electric motor and a gliding body 11 at the rear end of an movable arm. A switch 20 which is activated by the movement within the gliding body of the spring holding member is connected to the electric motor through a motor driver 21 to control the electric motor, and the applying force control of the spot welding gun driven by the electric motor is executed.