An electric spot welding gun (10) includes: a servo motor (40); a push rod (50) that advances and retracts in response to rotation of a rotor (43) of the servo motor; a drive-side electrode tip (71) that is mounted to a drive-side arm (70) fixed to a leading end of the push rod; and an encoder (60) that detects the rotation angle of the rotor of the servo motor, the position of the electrode tip being offset relative to the push rod, in which the rotor and the encoder are disposed in parallel to each other in an offset plane on which the electrode tip is offset relative to the push rod, at an attitude in which a trailing end (44) of the rotor on a side opposite to a push rod side thereof and an input end (64) of the encoder are facing in the same direction.