Automatic brake system of motor vehicle

When it is judged that a possible collision of the own vehicle with a preceding vehicle is avoidable by operation of either one of the brake pedal and steering wheel, a first grade braking force is automatically produced. When it is judged that the possible collision is unavoidable by operation of either of the brake pedal and steering wheel, a second grade braking force (FH) is automatically produced, which is greater than the first grade braking force (FL).