The invention relates to a hydraulic power control device notably for a vehicle powered braking system, having yielding lever means. The lever means comprise an arm pivotally mounted on a first axle secured to the device housing, and a feeler member pivotally mounted on a second axle, said second axle being pivotally mounted on the arm, the ends of the feeler member cooperating with a spool valve and a servomotor piston respectively, the connection between the arm and the housing being yieldable in case of excessive stresses applied on a push rod engaging the free end of the arm.