A spot welded joint comprising a plurality of steel sheets (1A, 1B, 1C), these sheets (1A, 1B, 1C) being joined by a nugget and a heat affected zone, wherein the joint is formed by superposing and spot welding the plurality of steel sheets (1A, 1B, 1C), wherein at least one steel sheet (1A, S1) of the plurality of steel sheets (1A, 1B, 1C) is a high strength steel sheet (1A, S1) with a tensile strength of 750 MPa to 2500 MPa; a carbon equivalent Ceq of the high strength steel sheet (1A, S1) expressed by the following formula is 0.20 mass% to 0.55 mass%; in the superposing of the plurality of steel sheets (1A, 1B, 1C), the high strength steel sheet (1A, S1) is arranged at an outermost side, the high strength steel sheet (1A, S1) arranged at the outermost side being defined as a "high strength steel sheet (1A, S1)", and being characterised by the following: a cross-section cut along the sheet thickness direction of the steel sheet while passing through a center of a welding mark formed on the surface of the steel sheet due to the spot welding, when defining superposed surfaces of the high strength steel sheet (1A, S1) and another steel sheet superposed with that high strength steel sheet (1A, S1) as a "plane " and when defining a plane passing through a point of one-half of a distance between a crossing point of a line in the sheet thickness direction passing through the center of the nugget and a line showing the end of the nugget at the high strength steel sheet (1A, S1) side and a crossing point of the plane and the line and parallel to the plane as a "plane ", a square area, which has sides of 30 μm centered about a crossing point of a line separated from a tangent at any position on a nugget end line sandwiched between the plane and the plane in the line showing the end of the nugget by 250 μm to a heat affected zone side and parallel to that tangent and a line passing through the any position and vertical to the line, is contained in a heat affected zone having the high strength steel sheet (1A. S1) as a base material; and in the square area, an average value of widths of blocks comprised of lath martensite is 0.5 to 7.0 μm Ceq = C + Si / 30 + Mn / 20 + 2 P + 4 S in the formula., [Si], [Mn],, and respectively being contents of C, Si. Mn, P, and S (mass%). a cross-section cut along the sheet thickness direction of the steel sheet while passing through a center of a welding mark formed on the surface of the steel sheet due to the spot welding, when defining superposed surfaces of the high strength steel sheet (1A, S1) and another steel sheet superposed with that high strength steel sheet (1A, S1) as a "plane " and when defining a plane passing through a point of one-half of a distance between a crossing point of a line in the sheet thickness direction passing through the center of the nugget and a line showing the end of the nugget at the high strength steel sheet (1A, S1) side and a crossing point of the plane and the line and parallel to the plane as a "plane ", a square area, which has sides of 30 μm centered about a crossing point of a line separated from a tangent at any position on a nugget end line sandwiched between the plane and the plane in the line showing the end of the nugget by 250 μm to a heat affected zone side and parallel to that tangent and a line passing through the any position and vertical to the line, is contained in a heat affected zone having the high strength steel sheet (1A. S1) as a base material; and in the square area, an average value of widths of blocks comprised of lath martensite is 0.5 to 7.0 μm Ceq = C + Si / 30 + Mn / 20 + 2 P + 4 S in the formula., [Si], [Mn],, and respectively being contents of C, Si. Mn, P, and S (mass%).