A hydraulic pressure control valve for a dual-circuit brake system of a vehicle. In this control valve a pair of valve pistons for controlling the braking hydraulic pressure delivered to each of rear wheel brakes are disposed in a housing parallelly and imparted with biasing force directed inwards of the housing by one biasing device. The biasing device is assembled or set within a cover of cup-shape such that the biasing device has been given a preload substantially equal to a biasing force necessary for the control valve before the cover is fixed to the valve housing. The biasing device includes a swingable guide rod attached at one end thereof to the cover with a pivot pin, a sliding member slidably fitted on the guide rod, and a compression spring disposed between the sliding member and a free end of the guide rod for biasing the sliding member toward the pivoted end of the guide rod. The guide rod is provided with a projection for stopping axial movement of the sliding member due to the biasing force of the spring. When the cover is attached to the valve housing the sliding member abuts on ends of the valve pistons and consequently is separated from the projection for transmitting the biasing force of the spring to the valve pistons.