Spot welded joint and spot welding method

A spot welding method comprising:

• superposing at least two steel sheets;
• forming a melt zone by conduction,
• wherein the conduction is performed by running a current having a value,
• after said melt zone forming, forming a solidified structure in the melt zone running another current of which value is lower than the value for forming the melt zone, and applying an electromagnetic vibration, and
• wherein a frequency fV of the electromagnetic vibration, a solidification speed νS when the melt zone solidifies, and an arm interval of dendrites λD when the melt zone solidifies satisfy 0.2≤νS/(λD·fV)≤4.0, and
• the solidification speed νS and the arm interval of the dendrites λD are obtained by advance experiments, wherein:
• the solidification speed νS and the arm intervals of the dendrites λD are obtained by applying spot welding to samples of which combination of sheet and type of steel are the same as in the steel sheets to be welded while putting time of running current under plural conditions.