An actuator for use in a vehicle hydraulic brake system having an anti-lock control and/or vehicle stability control function has a housing which also serves as the body of the master cylinder. The housing is formed with four wheel cylinder ports to be connected to the respective wheel cylinders through pipes. Since there is usually enough space in front of the housing, all of the wheel cylinder ports are formed in the front end face of the housing so that the pipes can be arranged in the large space in front of the actuator. The ports are arranged in the width direction of the vehicle with the ports at both ends located at a higher level than the other ports. With this arrangement, pipes can be easily mounted to and dismounted from the ports at both ends by turning a spanner without the possibility of the spanner interfering with components in the engine room, such as a relay box or the engine.