To conduct impact prevention to a work and to maintain welding pressure of a prescribed value for the work by, for example, quickly traveling a movable electrode of spot welding equipment, stopping after traveling/reaching to the surface of the work, further, quickly shifting an operation state to a pressurized state.

A work W is subjected to spot welding by a movable electrode S, which by controlling a double action type cylinder mechanism 1 with a control mechanism 20, reciprocating a sub-cylinder 6 with a main cylinder 2 and is connected to a position rod 9 of the sub-cylinder 6, together with a fixed electrode F. At this time, the sub cylinder 6 is advanced against repulsion force by supplying a working fluid to the main cylinder 2, at the moment the movable electrode S reaches the surface of the work W, advancing of the sub-cylinder 6 is stopped and the movable electrodes S maintains the pressurized state of a prescribed value for the surface of the work W by relatively adjusting a supplying quantity to the cylinders 2, 6 respectively. After welding is completed, the working fluid is discharged from the cylinders 2, 6, the piston 4, 8 are returned to the original position respectively with a return spring 5, a buffer return spring 10 and prepared for a next operation.