Patent ID: 7607300

Claim:
A fluid pressure booster comprising: a control piston in which brake operation input from a brake operation member acts in an advancing direction, and reaction based on fluid pressure of a booster fluid pressure generation chamber that generates fluid pressure for actuating a master piston of a master cylinder acts in a retracting direction; a pressure increasing valve provided between the booster fluid pressure generation chamber and a fluid pressure generation source so as to open at the time of advance of the control piston and close at the time of retraction of the control piston; and a pressure reducing valve provided between a release chamber communicating with a reservoir and the booster fluid pressure generation chamber so as to close at the time of the advance of the control piston and open at the time of the retraction of the control piston, the control piston being actuated forward and backward so that the brake operation input and the reaction based on the fluid pressure in the booster fluid pressure generation chamber are balanced to regulate the fluid pressure in the fluid pressure generation source to act on the booster fluid pressure generation chamber, wherein the pressure increasing valve includes first valve means and second valve means that sequentially open according to an increase in the brake operation input, and a seal diameter of the second valve means is larger than that of the first valve means, and wherein an operation rod that is coaxially slidable in the first valve means controls the sequential opening and closing of the first and second valve means, and an end of the operation rod facing the control piston includes a valve portion by which the pressure reducing valve is closable.