To rapidly program the coordinate values of the welding and spotting position of a robot gun for spot welding.

A moving side electrode 6 is previously provided with a contacless detector S for measuring the distance between the electrode and a work. The distance from the detector to the top end of the tip of a stationary side electrode 8 is previously set as a reference value A. The distance from the spotting position of the work is measured by the detector every time the robot gun is successively moved to the work spotting position W1...Wn. The measured values a...n and the reference value A are compared and the displacement rates Aδ1...Δn. of the pressurization direction occurring between the stationary side electrode 8 and the work are determined. These displacement rates are fed back to a robot controller 9 and the position control meeting the displacement rates measured at every spotting position is executed in such a manner that the top end of the tip of the stationary side electrode 8 comes into zero touch with the work spotting position, by which the position data acting on the coordinate values of the spotting point of the robot welding gun is taught.