PURPOSE: To decrease the number of part items, to eliminate the need for mounting space, and to achieve further cost reduction by eliminating the need for a pressure source exclusively for automatic braking.

CONSTITUTION: During automatic braking, an ECU 36 restricts an electric- controlled variable throttle 25, thus generating pressure in power-steering operating fluid. This pressure causes closing of first and second brake passage switching valves 18, 19, and also causes lowering of the first and second pistons 30a, 31a of first and second automatic brake cylinders 30, 31, thereby generating brake pressure for the automatic braking. This brake pressure is supplied to first to fourth wheel cylinders 6, 7, 13, 14 via seventh and eighth passages 28, 29, first and second passages 8, 15 and via first to fourth branch passages 9, 10, 16, 17 so that first to fourth wheels 4, 5, 11, 12 are braked automatically with braking forces that match the amount of restriction of the electric- controlled variable throttle 25. Thus the need for a pressure source exclusively for automatic braking is eliminated.