In a variable ratio steering system of a vehicle with a variable steering ratio mechanism varying a steering ratio R of steering wheel angle .theta..sub.S to road wheel steer angle .theta..sub.W at steered road wheels, a vehicle speed sensor, and a steering angle sensor, a steering ratio control unit controls the steering ratio according to a fixed steering ratio characteristic when the steering wheel angle .theta..sub.S is less than or equal to a predetermined angle .theta..sub.1 substantially corresponding to a neutral position of a steering wheel. Conversely when the steering wheel angle .theta..sub.S is greater than the predetermined angle .theta..sub.1 substantially corresponding to the neutral position of the steering wheel, the steering ratio control unit controls the steering ratio according to a vehicle-speed dependent steering ratio characteristic that a steering angle versus road wheel steer angle characteristic varies depending on a vehicle speed value.