SPOT WELDING SYSTEM, METHOD AND COMPUTER PROGRAM CAPABLE OF MAKING PRESSURIZING FORCE APPLIED TO OBJECT TO BE PRESSED TO BE CONSTANT

In a conventional spot welding gun, since pressurizing force due to a movable electrode is measured by a pressure sensor at each of a plurality of attitudes, calibration work is complicated. A spot welding system 10 includes a spot welding gun having an opposite electrode 44, a movable electrode 48, and a drive part 52, a position detection part 54 that detects a position of the movable electrode 48, and a pressure change calculation part that calculates an amount of change between first pressurizing force at a first attitude and second pressurizing force at a second attitude based on a first position of the movable electrode 48 when the drive part 52 has been driven by a first pressurizing force command at the first attitude, a second position of the movable electrode 48 when the drive part 52 has been driven by the first pressurizing force command at the second attitude, and the first pressurizing force command. The first pressurizing force command and the first pressurizing force coincide with each other.