A brake booster for a vehicle is provided. The booster includes a casing formed by a combination of a front and rear shell. A diaphragm divides the casing into a constant and a variable pressure room. A circumference of a front side end seals a valve body combined with the diaphragm and a rear portion penetrates the rear shell. A high pressure air passage selectively provides high pressure air from the rear portion to the variable pressure room and a bypass passage selectively provides atmospheric air to the variable pressure room. A check valve provides high pressure air passed a turbo charger and an intercooler to the variable pressure room through the high pressure air passage. An input rod advances and retreats through an air valve of the valve body. An output rod delivers force based on displacement of the air valve and the diaphragm to a master cylinder.