A control system suitable for an electric power steering system comprising: an electric motor; a speed reducer that amplifies motor torque generated by the electric motor; a basic motor torque command value computation unit that computes a basic motor torque command value (Tb) for the electric motor; an external torque specifying unit that specifies external torque that is applied to the speed reducer and that is other than the motor torque; a motor angular velocity computation unit that computes an angular velocity of the electric motor with use of a model formed on an assumption that friction is not generated in the speed reducer or with use of a model obtained by modifying the model formed on the assumption that friction is not generated in the speed reducer, based on an actually-measured motor angular velocity; a friction compensation control unit that estimates friction to be compensated for, with use of the external torque specified by the external torque specifying unit, the angular velocity computed by the motor angular velocity computation unit, the basic motor torque command value (Tb) computed by the basic motor torque command value computation unit, and a simulation model of the control system in which the friction to be compensated for is taken into account, said friction to be compensated for including at least friction generated in the speed reducer out of friction generated in the control system; a motor torque command value computation unit that computes a motor torque command value that is a target value of the motor torque to be generated from the electric motor, with use of the friction estimated by the friction compensation control unit and the basic motor torque command value (Tb) computed by the basic motor torque command value computation unit; and a controller that controls the electric motor based on the motor torque command value computed by the motor torque command value computation unit. an electric motor; a speed reducer that amplifies motor torque generated by the electric motor; a basic motor torque command value computation unit that computes a basic motor torque command value (Tb) for the electric motor; an external torque specifying unit that specifies external torque that is applied to the speed reducer and that is other than the motor torque; a motor angular velocity computation unit that computes an angular velocity of the electric motor with use of a model formed on an assumption that friction is not generated in the speed reducer or with use of a model obtained by modifying the model formed on the assumption that friction is not generated in the speed reducer, based on an actually-measured motor angular velocity; a friction compensation control unit that estimates friction to be compensated for, with use of the external torque specified by the external torque specifying unit, the angular velocity computed by the motor angular velocity computation unit, the basic motor torque command value (Tb) computed by the basic motor torque command value computation unit, and a simulation model of the control system in which the friction to be compensated for is taken into account, said friction to be compensated for including at least friction generated in the speed reducer out of friction generated in the control system; a motor torque command value computation unit that computes a motor torque command value that is a target value of the motor torque to be generated from the electric motor, with use of the friction estimated by the friction compensation control unit and the basic motor torque command value (Tb) computed by the basic motor torque command value computation unit; and a controller that controls the electric motor based on the motor torque command value computed by the motor torque command value computation unit.