To improve quality control of welding, there is included in resistance welding: a magnetic field measuring unit (205) disposed around a welded part and configured to measure a local current at the welded part; a high-speed camera (202) configured to capture an image for measuring local temperature at the welded part from variation of luminance of emission by capturing light emission state of the welded part; a comparison determination unit (106) configured to determine whether or not at least one of current information and temperature information has an abnormal value by comparing the current information calculated based on magnetic field information acquired from the magnetic field measuring unit with past current information and comparing the temperature information measured from an image of the high-speed camera (202) with past temperature information.