In the conventional electric power steering control system, a gain by which an approximate differentiation value of a torque signal is multiplied comes to be large at high speed driving. Therefore, a problem exits in that unstable feel of steering increases, thereby steering convergence getting worse. An electric power steering control system includes a variable type torque differential operation device 104A that makes variable a differential time constant at the time of outputting a second motor current, and a time constant determining device 105X that commands the time constant to the variable type torque differential operation device 104A. The time constant determining device 105X determines the time constant in response to any change in not less than one signal selected and used in an arbitrary manner out of a speed signal 81, a torque signal 82, a yaw rate signal 83 and a steering rate signal 84.