A pressure regulator for hydraulically controlled machine tools comprises a first directly controlled three-way pressure-regulating valve with which required work pressure can be set by a machine control system. In addition to a first surface, the control spool is provided with a second surface to which hydraulic fluid under the pressure at the pressure port can be applied by means of an externally controllable valve. This results in an additional force acting upon the control spool in the direction opposite to, or in the direction of, the force exerted by the elastic element on the control spool.