This brake hydraulic control actuator increases ability to reserve the leaked brake fluid and degree of freedom for the structural layout in the actuator body. The bottom surface of the actuator body (10) having the cylinder bores (43) of the low pressure reservoirs (40) and (41) thereon is closed and sealed by the pot plate (20), and the pocket (23), which projects toward the direction to depart from the bottom surface, is formed in the pot plate (20).