PURPOSE: To secure an antiskid function in an easy manner, by making both proportional decompression valves open simutaneously in time of a rear wheel being locked, in case of a device which feeds a rear wheel brake with such hydraulic pressure as being more compressed than working hydraulic pressure in a front wheel brake via a couple of proportional decompression valves.

CONSTITUTION: Hydraulic fluid produced in a master cylinder is fed to each of symmetrical rear wheel brakes via each primary braking hydraulic pressure chamber, oil passages 6a and 6b, each of first and second decompression valves Va and Vb, and oil passages 7a and 7b of both first and second braking hydraulic pressure regulating devices. In this case, pistons 30 being energized in a valve closing direction by means of a spring 6 is installed in each proportional decompression valve. Both these pistons 30 are installed in parallel with each other, while a control cylinder part 41 is set up in parallel between both valves Va and Vb. And, each of these pistons 30 is shiftably coupled to a coupling member 43 locked to a control piston 42 operated by antiskid control hydraulic pressure by a slight distance δ relatively with the conrol piston 42.