A vacuum booster device includes a housing, a movable partition mounted within the housing, a valve piston mounted at the housing in a movable manner, an input member, an output member, a reaction force member, a control valve including an air control valve portion and a negative pressure control valve portion, a key member specifying a limit of a movement of the input member relative to the valve piston in a front and rear direction, and a straightening portion arranged in an air passage that is formed between the input member and the valve piston and that is positioned at a front of the air valve portion and the air control valve portion, the straightening portion being formed into a shape to be prevented from projecting relative to an outer diameter portion of the air valve portion and arranged forward relative to the air valve portion by a predetermined distance.