Simple shear tests and hydraulic bulge tests of IF steel sheet, 590 and 980 MPa grade dual phase high strength steel sheets were carried out to investigate the work-hardening behavior, i.e. equivalent stress-equivalent plastic strain curves and Instantaneous n-values, in large strain region over uniform elongation. Parameter κ that correlates simple shear (or bulge) stress to uniaxial tensile stress used to obtain the equivalent stress-equivalent plastic strain curve. The work-hardening behaviors obtained by simple shear tests and bulge test were good agreement with those of uniaxial tensile test. On the other hands, work-hardening equations proposed by previous studies were less likely to reproduce behaviors of the Instantaneous n-value, i.e. a strain dependency of the n-value, in a variety of steel sheets. Thus a new work-hardening equation that can reproduce the strain dependency of the n-value proposed. This equation can reproduce the work-hardening behavior of a variety of steel sheets.