Provided is a steel sheet which has a component composition including, in mass%, over 0.0060% but not more than 0.0100% of C, not more than 0.05% of Si, at least 0.05% but not more than 0.60% of Mn, not more than 0.050% of P, not more than 0.050% of S, at least 0.020% but not more than 0.050% of Al, over 0.0140% but not more than 0.0180% of N, and not more than 0.040% of Cr, the remainder being Feand unavoidable impurities. The steel sheet is provided with mechanical properties such as an aging index in the rolling direction of 25-55 MPa, and a yield strength of 620-700 MPa. Accordingly, thesteel sheet exhibits sufficient strength and excellent moulding properties, despite being thin.