hydraulic braking pressure control apparatus having a casing provided therein with an input hydraulic chamber for receiving a hydraulic pressure from a master cylinder , an output hydraulic chamber adapted to generate a hydraulic pressure to a wheel brake for actuation thereof in response to the input of the pressure to the input hydraulic chamber , and a control chamber to be fed with a control liquid pressure for controlling the pressure output from the output hydraulic chamber in accordance with the condition of a wheel , wherein a valve mechanism is disposed between the input and output hydraulic chambers for cutting their mutual communication only when the liquid pressure is inducted into the control chamber and means is further provided for supplementing pressure oil to the output hydraulic chamber in reply to the reduction of the pressure therein below a set value . the supplementary pressure oil is supplied from the master cyinder through a throttle .