High strength low specific gravity steel sheet excellent in spot weldability

The steel sheet is, by mass%, C: 0.100% than 0.500% or less, Si: 0.0001% to less than 0.20%, Mn: 0.20%, greater than 0.50% or less, al: 3.0% or more, 10.0% or less, N: 0.0030% or more, 0.0100% or less, Ti: 0.100% than 1.000% or less, P: 0.00001% or more, 0.0200% or less, S: 0.00001% or more, containing 0.0100%, in mass%, the sum of the content of the C and the Ti is satisfied 0.200 specific gravity of 5.5 or more 7.5.