The invention relates to a device for regulating a pressurized gas, said device including: a stopper (4) engaging with a seat (5) and capable of closing a pressurized gas passage; a so-called low-pressure chamber (29) downstream from the seat (5), the low-pressure chamber including a plate (27) to which the stopper (4) is coupled, and the plate being subjected to the force of a spring (30) housed in said chamber (29) and arranged concentrically relative to the seat (5) and the fastening means (28) thereof. The chamber (29) is defined by a diaphragm (26) in free contact with the plate (27). The opposite surface of the diaphragm (26) is subjected to the force of a spring (20) having a prestress which is adjustable via control means (13, 14). The control means are indexed according to two positions: a first prestress release position for ensuring the closure of the device at the stopper (4), and a second calibrated prestress position of the diaphragm (26) corresponding to the regulator operational position. A sealed chamber (24) defined by the surface of the membrane (26) opposite the low-pressure chamber (29) is formed by the prestress control means for ensuring the connection to a detector for detecting the presence of a leak or of the used gas in order to detect a potential leak at the diaphragm.