A projection welded joint, the welded joint being formed by joining a steel sheet having a tensile strength of 980 MPa or higher and a nut by performing projection welding, wherein, in a hardness distribution from the steel sheet to the nut through a weld metal zone, each of a hardened region which exists on a side of the steel sheet with respect to a center of the weld metal zone and whose hardness S H1 is higher than a hardness S H0 of a base metal of the steel sheet and a hardened region which exists on a side of the nut with respect to the center of the weld metal zone and whose hardness N H1 is higher than a hardness N H0 of a base metal of the nut extends continuously for a distance of 500 μm or more, wherein, in the two hardened regions, a maximum hardness N Hmax in a weld heat affected zone on the side of the nut is higher than a maximum hardness S Hmax in a weld heat affected zone on the side of the steel sheet, wherein a region which has a center thereof at a position corresponding to the maximum hardness S Hmax in the weld heat affected zone on the side of the steel sheet and which extends for a distance of 500 μm in a direction parallel to a joint interface and a distance of 50 μm in a direction perpendicular to the joint interface is formed of a martensite microstructure having a prior austenite grain size of 20 μm or less, and wherein the steel sheet has a chemical composition containing, by mass%, C: 0.08% or more and 0.20% or less, Si: 0.2% or more and 1.6% or less, Mn: 1.0% or more and 3.4% or less, P: 0.05% or less, S: 0.01% or less, Al: 0.01% or more and 0.10% or less, N: 0.01% or less, one or more selected from Nb: 0.005% or more and 0.050% or less and Ti: 0.005% or more and 0.050% or less, and optionally further containing by mass%, one, two, or more selected from B: 0.0050% or less, V: 0.05% or less, Cr: 0.50% or less, Mo: 0.50% or less, Co: 0.50% or less, Cu: 0.50% or less, Ni: 0.50% or less, Sb: 0.020% or less, and Ca and/or REM: 0.0050% or less, and a balance of Fe and incidental impurities, wherein the nut is made of a steel grade having an equivalent carbon content of 0.20% or more that is calculated as below: equivalent carbon content (%) = C + Mn/6 + Si/24 + Ni/40 + Cr/5 + Mo/4 + V/14. wherein, in a hardness distribution from the steel sheet to the nut through a weld metal zone, each of a hardened region which exists on a side of the steel sheet with respect to a center of the weld metal zone and whose hardness S H1 is higher than a hardness S H0 of a base metal of the steel sheet and a hardened region which exists on a side of the nut with respect to the center of the weld metal zone and whose hardness N H1 is higher than a hardness N H0 of a base metal of the nut extends continuously for a distance of 500 μm or more, wherein, in the two hardened regions, a maximum hardness N Hmax in a weld heat affected zone on the side of the nut is higher than a maximum hardness S Hmax in a weld heat affected zone on the side of the steel sheet, wherein a region which has a center thereof at a position corresponding to the maximum hardness S Hmax in the weld heat affected zone on the side of the steel sheet and which extends for a distance of 500 μm in a direction parallel to a joint interface and a distance of 50 μm in a direction perpendicular to the joint interface is formed of a martensite microstructure having a prior austenite grain size of 20 μm or less, and wherein the steel sheet has a chemical composition containing, by mass%, C: 0.08% or more and 0.20% or less, Si: 0.2% or more and 1.6% or less, Mn: 1.0% or more and 3.4% or less, P: 0.05% or less, S: 0.01% or less, Al: 0.01% or more and 0.10% or less, N: 0.01% or less, one or more selected from Nb: 0.005% or more and 0.050% or less and Ti: 0.005% or more and 0.050% or less, and optionally further containing by mass%, one, two, or more selected from B: 0.0050% or less, V: 0.05% or less, Cr: 0.50% or less, Mo: 0.50% or less, Co: 0.50% or less, Cu: 0.50% or less, Ni: 0.50% or less, Sb: 0.020% or less, and Ca and/or REM: 0.0050% or less, and a balance of Fe and incidental impurities, wherein the nut is made of a steel grade having an equivalent carbon content of 0.20% or more that is calculated as below: equivalent carbon content (%) = C + Mn/6 + Si/24 + Ni/40 + Cr/5 + Mo/4 + V/14. C: 0.08% or more and 0.20% or less, Si: 0.2% or more and 1.6% or less, Mn: 1.0% or more and 3.4% or less, P: 0.05% or less, S: 0.01% or less, Al: 0.01% or more and 0.10% or less, N: 0.01% or less, one or more selected from Nb: 0.005% or more and 0.050% or less and Ti: 0.005% or more and 0.050% or less, and optionally further containing by mass%, one, two, or more selected from B: 0.0050% or less, V: 0.05% or less, Cr: 0.50% or less, Mo: 0.50% or less, Co: 0.50% or less, Cu: 0.50% or less, Ni: 0.50% or less, Sb: 0.020% or less, and Ca and/or REM: 0.0050% or less, and by mass%, one, two, or more selected from B: 0.0050% or less, V: 0.05% or less, Cr: 0.50% or less, Mo: 0.50% or less, Co: 0.50% or less, Cu: 0.50% or less, Ni: 0.50% or less, Sb: 0.020% or less, and Ca and/or REM: 0.0050% or less, and a balance of Fe and incidental impurities, wherein the nut is made of a steel grade having an equivalent carbon content of 0.20% or more that is calculated as below: equivalent carbon content (%) = C + Mn/6 + Si/24 + Ni/40 + Cr/5 + Mo/4 + V/14.