Abstract: Portable measuring instrument for measuring the clamping force between a pair of welding electrodes in spot welding. The instrument comprises a measuring cell (1) designed to be inserted between a pair of welding electrodes. The measuring cell contains a wire strain bridge for measuring the clamping force between the welding electrodes and a pair of electrodes (5) in a voltage detector for indicating the turning on of the welding current. The measuring cell is connected electrically to an electronic unit with optical indicating means (9), e.g. an LED stack, which indicates the magnitude of the clamping force when the welding current is turned on, and also the maximum clamping force attained during welding, and separately preserves the display of both of these values. The LED stack and the electronics are arranged in an apparatus casing (3).