A target relative rotational angle t which is created by a steering
gear ratio change unit and which is formed by a lower steering shaft relative to
an upper steering shaft is calculated on the basis of a steering angle ,
and a post-correction target relative rotational angle ta to be created
by the steering gear ratio change unit is calculated on the basis of the target
relative rotational angle t and a vehicle speed range that has been
determined on the basis of a vehicle speed V. Thus, a target relative rotational
angle in one lateral direction is so corrected as to be equal to or smaller than
a difference between a permissible rotational angle to be defined by a spiral cable
in the other lateral direction and a maximum possible rotational angle of the lower
steering shaft in the other lateral direction. An electric motor is controlled
on the basis of the post-correction target relative rotational angle ta.
