PURPOSE: To eliminate the noise of a welding current and to improve detecting accuracy of the electrode force by providing a welding current application finishing point detection means, an output detection means of an electrode force detection means and a means to store and calculate the output of the output detection means to the electrode force detection means.

CONSTITUTION: The electrode force detection means 5 is a circuit to detect the quantity of strain of the electrode which corresponds to a strain gage, etc. The welding current application finishing point detection means 6 corresponds to a means to detect the flow finishing points of time l1, l2... for every half cycle of a power source cycle and is constituted of a current transformer to detect a primary current of a resistance welding machine, a zero point detection circuit, etc., connected with the current transformer. The storage and arithmetic means 7 is a microcomputer to input and process detected signals of the current application finishing points l1, l2.... The output detection means 8 of the electrode force detection mean is constituted of a sample holding circuit and an A/D converter circuit, etc., connected therewith and corrects and operates the real electrode force data in a moment when the welding current finishes flowing for every half cycle and displays the corrected and operated data on a display or the analog data are displayed on a welding force display device 9 by an O/A converter incorporated in the storage and arithmetic means 7 to detect the electrode force.