A steering system, comprising: an input cylinder having a first hydraulic chamber and a second hydraulic chamber; a transmission mechanism, wherein a transmission efficiency for converting and transmitting a linear motion of the input cylinder to a rotary motion of a steering wheel is less than a transmission efficiency for converting and transmitting the rotary motion of the steering wheel to the linear motion of the input cylinder; an output cylinder connected to a steerable vehicle wheel and having a third hydraulic chamber and a fourth hydraulic chamber; a first hydraulic passage for connecting the first hydraulic chamber to the third hydraulic chamber; a second hydraulic passage for connecting the second hydraulic chamber to the fourth hydraulic chamber; a flow rate control mechanism for exchanging hydraulic oil with: a first hydraulic circuit including the first and third hydraulic chambers and the first hydraulic passage; and a second hydraulic circuit including the second and fourth hydraulic chambers and the second hydraulic passage, in order to adjust a ratio of hydraulic oil quantities in the first and second hydraulic circuits; a steering actuator for providing the steerable vehicle wheel with a steering power assistance; and a controller for cooperatively controlling the flow rate control mechanism and the steering actuator.