A first computing section stores a plurality of types of variable transmission ratio characteristics prescribed in correspondence with different modes in the form of maps. With reference to one of the maps corresponding to a selected one of the modes, the first computing section computes a first command angle by which the variable transmission ratio characteristics prescribed by the map are brought about. In this manner, variable gear ratio control is carried out. After a subsequent mode has been selected, the first computing section does not switch the maps which are referred to in the variable gear ratio control if the steering wheel turning angle θs is greater than or equal to a predetermined threshold value α.