A driving support ECU is configured to set, when a recognition state of a lane marker by a sensor is a one side lane marker recognizable state which is a state where the sensor can recognize only one of a left lane marker and a right lane marker, a steering angle guard value and/or a steering angle speed guard value to a value which is smaller than when the recognition state of the lane marker is a both lane markers recognizable state which is a state where the sensor can recognize both the left lane marker and the right lane marker.