A braking pressure control device for a brake system comprising a braking pressure generator (16), a wheel brake cylinder connected via a brake line (15) with the latter to actuate a brake (18), a braking pressure control circuit which is interposed into the brake line and comprising a piston pump, the outlet valve (9) of which is connectible to the brake line (15), and comprising solenoid operated brake control valves (19, 20), the inlet valve (8) and the outlet valve (9) of the piston pump are arranged on the pump housing (1), and the difference in pressure for opening the inlet valve (8) is such that the inlet valve (8) remains closed whenever the pressure in the return line (21) is below atmospheric pressure. An annular chamber (11) encircling the piston (3) is provided on the side of the slide seal (12) remote from the working chamber (7) of the piston pump, the annular chamber being sealed in relation to the eccentric piston drive housing portion ( 4) and communicating with a pump supply line connected to the brake pressure line (15), or with the return line (21) so as to supplied with fluid and prevent air from entering the working chamber through the piston clearance space.