Method of resistance spot welding and resistance spot welding apparatus

A resistance spot welding apparatus configured to weld a workpiece including two or more steel plates in an overlapping state, with a steel plate of the two or more steel plates being a high-tensile steel plate, the resistance spot welding apparatus including a first electrode and a second electrode, the first electrode being configured to be in contact with the high-tensile steel plate, the second electrode being configured to be in contact with an other steel plate of the two or more steel plates,

• the resistance spot welding apparatus being configured to cause a cooling rate of the high-tensile steel plate to be higher than a cooling rate of the other steel plate, the high-tensile steel plate having a tensile strength higher than a tensile strength of the other steel plate, and the cooling rate of the high-tensile steel plate and the cooling rate of the other steel plate being cooling rates at a time of welding,
• wherein the first electrode is cooled by circulation of a first coolant inside the first electrode and the second electrode is cooled by circulation of a second coolant inside the second electrode,
• wherein the first coolant configured to circulate in the first electrode has a thermal absorptivity higher than a thermal absorptivity of the second coolant configured to circulate in the second electrode, and
• wherein at least one of the high-tensile steel plate or the other steel plate is coated with zinc.