The present invention relates chiefly to a hydraulic brake booster comprising a motor, preferably an electric motor. The main subject of the invention is a hydraulic brake booster comprising a thrust chamber (76) receiving, on command, a pressurized hydraulic fluid that drives a hydraulic piston (78) that drives a piston of a master cylinder, characterized in that it comprises a source of pressurized hydraulic liquid (116) provided with an electric motor (88) driving a hydraulic fluid pressuring device. The invention applies notably to the automotive industry. The invention applies mainly to the braking industry.