PURPOSE: To reduce the size and weight of a stud welding gun and to easily and surely determine the position of the front end of a stud.

CONSTITUTION: A linear motor 3 consisting of stators 4, 5 and a moving element 8 movable in the major axis direction of the stud ST is disposed at a gun body 1 of the arc stud welding machine. This moving element 8 and a holder 12 holding the stud ST are connected and an operating switch 2 for controlling the electric power to the linear motor 3 is disposed. A detector 13 for detecting the moving quantity of the moving element and a driving machine control circuit for displacing the position of the holder 12 according to the set value of a moving quantity setter 21 are disposed. The driving mechanism of the holder is constituted as the direct acting mechanism by the linear motor to simplify the construction of the driving mechanism. The stud mounted on the holder is extremely easily pressed to an object to be welded by controlling the electric power to the linear motor.