A brake negative pressure generating device of a vehicle includes: an electrically-driven supercharger for drawing in, compressing, and supplying outside air; a vacuum chamber connected to an inlet opening of the electrically-driven supercharger and supplying negative pressure for brake force boosting; a negative pressure supply passage for connecting the inlet opening of the electrically-driven supercharger and the vacuum chamber; and a first negative pressure control valve for opening and closing an inlet passage. Accordingly, the electrically-driven supercharger is run to supplement brake negative force if the brake negative force is not sufficient.