Abstract: A flat, electrically and thermally conductive flat surface group is formed in the common connection region 32 of the secondary coil 13. The flat conductive surface group is directly and mechanically joined to the connecting surfaces of the first conductor plate 42, the second conductor plate 44, and the third conductor plate 46, respectively. The first conductor plate 42, the second conductor plate 44, and the third conductor plate 46 cover the entire common connection region 32. The annular first conductor plate 42 occupies the maximum area. The refrigerant can be circulated in the annular cavity provided inside the first conductor plate 42 to efficiently cool the whole.

Abstract: The first database 38 outputs the welding current 44, the energization time 46, and the pressing force 48, etc. corresponding to the basic elements 32 including the kind of material, the thickness of material and the type of electrode. The second database 40 outputs the trend formula 52 used for correcting the output from the first database 38 depending on the property of the additional element 34. The element selecting device 36 selects an element and performs searching in the databases 38 and 40. The operating device 42 executes a correction operation process for applying the search result in the second database 40 to the search result in the first database 38, and outputs the welding condition 50 including the welding current 44, the energization time 46, and the pressing force 48.

Abstract: A flat, electrically and thermally conductive flat surface group is formed in the common connection region 32 of the secondary coil 13. The flat conductive surface group is directly and mechanically joined to the connecting surfaces of the first conductor plate 42, the second conductor plate 44, and the third conductor plate 46, respectively. The first conductor plate 42, the second conductor plate 44, and the third conductor plate 46 cover the entire common connection region 32. The annular first conductor plate 42 occupies the maximum area. The refrigerant can be circulated in the annular cavity provided inside the first conductor plate 42 to efficiently cool the whole.