An anti-skid braking control system which includes an actuator disposed in a braking fluid pressure circuit for controlling a braking fluid pressure. The actuator includes a body having a cylinder with one end closed by a closure member, an inlet port defined in the body and opening into the cylinder, the inlet port being connected through the braking fluid pressure circuit to a brake master cylinder, an outlet port defined in the body and opening into the cylinder, the outlet being connected through the braking fluid pressure circuit to a wheel brake actuating cylinder, a first valve disposed centrally in the cylinder between the inlet and outlet ports for cutting off fluid communication therebetween, a first piston disposed in one side of the cylinder and having an end on which a power fluid pressure from a fluid pressure source acts and an opposite end exposed in the braking fluid pressure circuit for engaging the first valve, the first piston being responsive to the power fluid pressure for moving the first valve to vary the volume of the braking fluid pressure circuit, a second piston disposed in an opposite side of the cylinder and having an end on which the power fluid pressure acts and actuatable by the braking fluid pressure in response to failure of the power fluid pressure, and a second valve for communicating the inlet and outlet ports directly with each other in response to operation of the second piston.