Abstract: In the negative pressure booster equipment of this invention, the vacuum passage to provide the communication between the control valve and the constant pressure chamber is furnished with a groove formed by the forming die of the valve body.According to the present invention, therefore, the groove is formed as the vacuum passage when the valve body is formed by a forming die of the valve body. By this groove, the sectional area of the vacuum passage is enlarged, and the air in the variable pressure chamber flows in larger quantity toward the constant pressure chamber. This causes the rapid restoration of vacuum pressure in the variable pressure chamber, and the power piston is promptly returned to the non-operating position. Because the groove is formed by a forming die, the portion with the groove is not enlarged.