Abstract: Disclosed is an antilock braking device including a first braking hydraulic adjusting member actuated so as to restrain braking oil pressure of wheel cylinders individually corresponding to left and right front wheels in response to antilock braking oil pressure for front wheels; a second braking hydraulic adjusting member actuated so as to restrain braking oil pressure of wheel cylinders individually corresponding to left and right rear wheels in response to antilock braking oil pressure for rear wheels; an antilock control system having a reservoir and a pump for pressurizing control oil from said reservoir to generate said antilock control oil pressure; and a tandem type master cylinder having a pair of output ports independent of each other connected to said both braking hydraulic adjusting members to generate braking oil pressure of each of said wheel cylinders, characterized in that a proportional reducing valve is interposed between both braking hydraulic adjusting members in order to supply braking oi

Abstract: The diaphragm of a vacuum booster device is normally placed in intimate contact with the disc portion of the booster piston due to the pressure difference between the first and second working chambers. The diaphragm has through-holes which the tie rods penetrate, and the peripheral portion of each through-hole is resiliently pushed to the disc portion of the booster piston by means of an elastic member. When the booster piston is manually operated while no vacuum pressure is stored in the first working chamber, the air in the first working chamber compressed by the advance of the booster piston is discharged into the second working chamber through the through-hole of the diaphragm, thus insuring smooth manual operation of the booster piston.