PURPOSE: To maintain comfortable operability by considering an organismic characteristic when a vehicle is put in a stable travel condition as well as to secure maneuvering stability.

CONSTITUTION: A control device has a rear wheel steering control means 30a to control a rear wheel steering angle according to a reference steering ratio, motional condition detecting means 31 to 33 to detect a motional condition quantity of a vehicle or a driver and a stable travel condition discriminating means 50a to discriminate a stable travel condition according to the motional condition quantity. A fluctuation quantity operation means 60a is arranged to carry out operation on a fluctuation quantity according to a frequency set at random, and when the vehicle is put in a stable travel condition, a correcting means 70a corrects the reference steering ratio so as to vary according to the fluctuation quantity, and imparts fluctuation forcibly to turning motion of the vehicle. When unstabilizing factor detecting means 31, 34 and 35 detect the occurrence of a factor to unstabilize vehicle motion, a correction prohibiting means 71 prohibits correction. The fluctuation may be forcibly imparted to throttle opening by applying throttle control.