Abstract: A pull-type booster includes a hollow body in which a movable wall is movably received to divide an interior thereof into a negative pressure chamber and a pressure-variable chamber. The movable wall has a tubular portion extending outwardly of the body and having an axial internal bore. The tubular portion is disposed in a room or chamber. A tubular cover member is mounted around the tubular portion to cover it and has an inlet in communication with the internal bore. An air tube has one end connected to the inlet, and the other end of the air tube is disposed outside of the room.