Provided is a steel sheet having a tensile strength of 980 MPa or more and exhibiting a high yield ratio and an excellent workability. The steel sheet includes C, Si, Mn, B, at least one of Ti, Nb and V, P, S, Al and N, the content by percentage of each of which is in a specified range. The metal structure thereof includes bainite, and martensite and may include ferrite. The proportion by area of bainite in the entire metal structure is 42 to 85%, that of martensite is 15 to 50%, that of ferrite is 5% or less, and that of entire microstructure of the balance other than bainite, martensite and ferrite is 3% or less thereof. Furthermore, bainite has an average crystal grain diameter of 7 mum or less.