A flow regulator, suitable for use in a respirator/ventilator, has a conduit through which a medium flows whose flow is to be regulated and a choke valve arranged outside the conduit. The choke valve includes a first solenoid, a pressure actuator that is moved by the shaft end of the first solenoid, and a fixed element with the conduit disposed between the pressure actuator and the fixed element. Actuation of the first solenoid displaces the pressure actuator so as to alter the cross-section of the conduit. The shaft of the first solenoid exhibits an effective stroke length so that the pressure actuator, in a first limit position, leaves the flow cross-section of the conduit unaltered and, in a second limit position, partially compresses the conduit against the detent. The flow regulator is made lightweight and inexpensive and also has a comparatively low power consumption by using a second solenoid having a shaft which exhibits a short effective stroke length compared to the shaft of the first solenoid. In the end position shaft of the second solenoid exerts a pressure against the pressure actuator so as to compress the conduit further than the compression produced by the first solenoid and thereby to entirely suppress the flow.