Abstract: The regulator is suitable for use in a breathing apparatus, particularly for aircraft, whose oxygen source consists of an open loop generator delivering oxygen-rich air under a low and variable overpressure. It comprises a respiratory gas inlet and an outlet for connection to a breathing mask. Communication between the inlet and outlet is controlled by at least two main piloted valves located in parallel flow relation and subjected to the pressure prevailing in a same control chamber. The control chamber is continuously connected to the inlet by a restriction and it is connected to the outlet by a pilot valve controlled by the pressure at the outlet. The restriction is preferably variable responsive to the inlet pressure.