The present invention is provided with: a main control unit 731 which is provided to a vehicle equipped with a steering angle changing mechanism 83 for changing the steering angle, and a motor 82 foroperating the steering angle changing mechanism 83, and which, after the position of the vehicle has reached a deviation start position at which deviation of the vehicle is started in order to suppress departure of the vehicle from a lane, outputs a main control signal expressing a main control amount for causing the motor 82 to generate assist torque for changing the steering angle; and a pre-control unit 732 which, when the position of the vehicle is located further towards the side of the centre of the lane than the deviation start position, outputs a pre-control signal expressing a pre-control amount for causing the motor 82 to generate assist torque equal to or lower than the frictional torque of the steering angle changing mechanism 83, until the main control unit 731 outputs the main control signal.