The influence of the erased state of a recording medium on the read response of a GMR head was investigated using a micromagnetic simulator that takes into account the full interaction between a GMR head and a double-layered medium. The calculated results clearly showed that a baseline shift occurs for a dc-erased medium. In addition, the magnetization configurations in the shields and the soft underlayer (SUL) result in complicated roll-off properties: the amplitudes of the output signal was increased by suppressing the longitudinal bias field strength when the vortex magnetizations in the shield and SUL rotate counter-clockwise, and vice versa.