Negative pressure booster and brake booster using the same

A negative pressure booster comprising:

• an input shaft which is applied with input;
• a valve body disposed so as to be capable of moving forward and backward with respect to a rear shell of a space;
• a power piston provided in the valve body for sectionalizing the space between a front shell and the rear shell into a constant pressure chamber in which a negative pressure is introduced, and a variable pressure chamber in which the atmosphere is introduced during operation;
• an output shaft connected to the valve body for outputting an output generated by the power piston and being boosted from the input via the valve body;
• a valve plunger connected to the input shaft and disposed in the valve body so as to be capable of sliding therein;
• a vacuum valve for controlling communication or blocking between the constant pressure chamber and the variable pressure chamber by the operation of the valve plunger;
• an atmosphere valve for controlling blocking or communication between the variable pressure chamber and at least the atmosphere;
• and
• an expandable and contractible boot provided between the rear shell and the input shaft,
• wherein the boot includes an accordion portion provided on the a side of the boot being connected to the rear shell so as to be expandable and contractible, and a rear end portion provided continuously from the accordion portion toward the rear,
• wherein a valve-body-side fixed portion is provided between the accordion portion and the rear end portion of the boot, an input-shaft-side fixed portion is provided at a rear end of the boot at a position rearward of the valve-body-side fixed portion, the valve-body-side fixed portion is fixed to or axially engaged with the valve body, and the input-shaft-side fixed portion is fixed to the input shaft, and
• wherein a predetermined number of atmosphere inlet ports are formed at a portion of the boot between the valve-body-side fixed portion and the input-shaft-side fixed portion.