A steering system comprising: a first steering device configured to change an angle of left and right chassis frame components of a suspension device to which left and right wheels that serve as front wheels of a vehicle are mounted so as to steer the left and right wheels that serve as the front wheels of the vehicle in accordance with a steering command angle (δ h) given by rotation of a steering wheel or an electrical signal, the left and right wheels being mechanically associated with each other; a second steering device configured to drive a supplementary turning actuator provided to each of the left and right wheels to change angles of the wheels relative to the chassis frame components and thereby individually turn the left and right wheels; and a vehicle information detection section configured to detect vehicle information including a vehicle velocity of the vehicle and the steering command angle (δ h), wherein the second steering device includes a supplementary turning control section configured to control the supplementary turning actuator so as to perform turning by a steering angle (δ 2) for auxiliary turning that is a difference between a steering angle (δ) of the front wheels, determined by a numerical model of vehicle motion on the basis of the information on the steering command angle (δ h) and the vehicle velocity, and an actual steering angle (δ 1) of the front wheels steered by the first steering device, and characterised in that the following equation is used in a control in which the steering angle (δ hb) for auxiliary turning is calculated by the supplementary turning control section of the second steering device and is used for turning: δ hb = 1 2 k 1 − k 2 + α k 1 + k 2 lh l r d a y δ with: k 1 = 1 − 1 − B l r l V 2 1 + AV 2 − d 2 l δ, k 2 = 1 − 1 − B l r l V 2 1 + AV 2 + d 2 l δ A = − m 2 l 2 l f K f − l r K r K f K r, B = − ml f 2 ll r K r where δ: steering angle of front wheel δ hb: hub steering angle (right) -δ hb: hub steering angle (left) d: tread l: distance between front wheel axle and rear wheel axle (l f + l r) l f: distance between the center of gravity and the front wheel axle lr: distance between the center of gravity and the rear wheel axle m: inertial mass of vehicle V: vehicle speed h: height of center of gravity from the ground α: front-axle lateral load transfer rate parameter, Kf and Kr: tire cornering power per one front wheel and one single rear wheel. a first steering device configured to change an angle of left and right chassis frame components of a suspension device to which left and right wheels that serve as front wheels of a vehicle are mounted so as to steer the left and right wheels that serve as the front wheels of the vehicle in accordance with a steering command angle (δ h) given by rotation of a steering wheel or an electrical signal, the left and right wheels being mechanically associated with each other; a second steering device configured to drive a supplementary turning actuator provided to each of the left and right wheels to change angles of the wheels relative to the chassis frame components and thereby individually turn the left and right wheels; and a vehicle information detection section configured to detect vehicle information including a vehicle velocity of the vehicle and the steering command angle (δ h), wherein the second steering device includes a supplementary turning control section configured to control the supplementary turning actuator so as to perform turning by a steering angle (δ 2) for auxiliary turning that is a difference between a steering angle (δ) of the front wheels, determined by a numerical model of vehicle motion on the basis of the information on the steering command angle (δ h) and the vehicle velocity, and an actual steering angle (δ 1) of the front wheels steered by the first steering device, and characterised in that the following equation is used in a control in which the steering angle (δ hb) for auxiliary turning is calculated by the supplementary turning control section of the second steering device and is used for turning: δ hb = 1 2 k 1 − k 2 + α k 1 + k 2 lh l r d a y δ with: k 1 = 1 − 1 − B l r l V 2 1 + AV 2 − d 2 l δ, k 2 = 1 − 1 − B l r l V 2 1 + AV 2 + d 2 l δ A = − m 2 l 2 l f K f − l r K r K f K r, B = − ml f 2 ll r K r where δ: steering angle of front wheel δ hb: hub steering angle (right) -δ hb: hub steering angle (left) d: tread l: distance between front wheel axle and rear wheel axle (l f + l r) l f: distance between the center of gravity and the front wheel axle lr: distance between the center of gravity and the rear wheel axle m: inertial mass of vehicle V: vehicle speed h: height of center of gravity from the ground α: front-axle lateral load transfer rate parameter, Kf and Kr: tire cornering power per one front wheel and one single rear wheel. δ: steering angle of front wheel δ hb: hub steering angle (right) -δ hb: hub steering angle (left) d: tread l: distance between front wheel axle and rear wheel axle (l f + l r) l f: distance between the center of gravity and the front wheel axle lr: distance between the center of gravity and the rear wheel axle m: inertial mass of vehicle V: vehicle speed h: height of center of gravity from the ground α: front-axle lateral load transfer rate parameter, Kf and Kr: tire cornering power per one front wheel and one single rear wheel.