A steering assist system for a motorcycle includes an actuator configured to provide a steering torque to steering of a motorcycle. A target-torque calculation unit is configured to obtain a target-torque for the steering, on a basis of a state of the motorcycle. A torque detecting unit is configured to detect a steering torque. A torque control unit is configured to drive an actuator on a basis of a deviation between the target torque obtained from the target-torque calculation unit and the steering torque obtained from the torque detecting unit.