A hydraulic braking system includes a tandem master cylinder having a bore with an opening and a closed wall at opposite ends thereof which formed in a housing, a first piston slidably fitted in the bore so as to define a first pressure chamber and a first fluid chamber therein and operatively connected to a brake pedal, a second piston slidably fitted in the bore so as to define a second fluid chamber adjacent to the first pressure chamber and a second pressure chamber and operatively connected to the first piston. A normally open valve communicates with each piston so as to close passages formed in the each pistons and communication between each fluid chambers and each pressure chambers, respectively, when each piston is moved in response to the depression of the brake pedal. A power source generates a hydraulic power pressure. A dynamic hydraulic braking pressure generator generates the hydraulic power pressure supplied from the power source in response to depression of the brake pedal and outputs to the second fluid chamber. A plurality of wheel cylinders for braking respective road wheels are divided into a first group of wheel brake cylinders communicated with the first pressure chamber through one of dual hydraulic circuits and a second group of wheel brake cylinders communicate with the second pressure chamber through an another of the dual hydraulic circuits. A restrictor restricts the sliding distance of the second piston toward the first piston to at least a predetermined distance for closing the valve means. Due to such construction, the first stage idle stroke of the tandem master cylinder is shortened and the stroke of the brake pedal is shortened.