Abstract: After a vehicle has entered a curve, a deviation (Sch) between a target turning state quantity Td and an actual turning state quantity Ta is computed. In a stage in which Sch does not reach a predetermined value after the vehicle has entered the curve, the possibility of the vehicle traveling in the curve is judged to be low, and the reliability of the curve information Rc, Pc is judged to be low. In this case, a determination for prohibiting execution of control (So=0) is made. In a stage after Sch has reached the predetermined value, the possibility of the vehicle traveling in the curve is judged to be high, and the reliability of the curve information Rc, Pc is judged to be high. In this case, a determination for permitting execution of the control (So=1) is made. Deceleration control is started and executed only when a control start condition is satisfied, and the determination for permission is made.