Abstract: A brake booster device which includes a front shell having a circular outer periphery, a rear shell having a circular outer periphery and being connected with the front shell to form a booster housing, a power piston diaphragm member disposed within the housing and dividing the same into a constant pressure chamber and a variable pressure chamber, a first pair of opposed sleeve portions provided on the inner peripheral portion of the front shell and extending radially inwardly to thereby form a figure 8 shape in the interior of the front shell, a second pair of opposed sleeve portions provided on the inner peripheral portion of the rear shell and extending radially inwardly to thereby form a figure 8 shape in the interior of the rear shell and a rod member interconnecting each of the first and second pairs of sleeve portions and which is inserted thereinto.