Braking system

A braking system comprising:

• a booster having a housing;
• a power piston that divides an interior of said housing into a constant-pressure chamber and a variable-pressure chamber;
• a valve body supported by said power piston;
• and a valve mechanism provided in said valve body to control supply of a working fluid into said variable-pressure chamber by movement of a plunger connected to an input rod interlocked with a brake pedal, wherein a thrust that is produced in said power piston by a differential pressure produced between said variable-pressure chamber and said constant-pressure chamber on a basis of an operation of said valve mechanism is transmitted to an output rod, and part of a reaction force from said output rod is transmitted through a reaction member and said plunger to act on said input rod;
• a control valve provided in communication with said variable-pressure chamber of said booster to supply the working fluid into said variable-pressure chamber in response to a driving signal inputted thereto;
• a stroke detect or for detecting a stroke of said brake pedal;
• drive control means for said control valve that compares a stroke speed of said brake pedal based on a result of detection by said stroke detect or with a preset threshold value and, when said stroke speed exceeds said threshold value, outputs a driving signal to said control valve;
• and
• a reaction-adjusting mechanism that, when the part of reaction force from said output rod that is transmitted through said reaction member and said plunger to act on said input rod has reached a predetermined value, reduces a rate of increase of the reaction force acting on said input rod to a level lower than that before said predetermined value is reached.