Inverted gas pressure regulator including at least one so-called high-pressure gas inlet duct, at least one so-called low-pressure gas outlet duct leading from a downstream expansion chamber, a mobile regulation part on one side of which the low pressure is exerted and on the other side of which a spring element bears, and which is adapted to shut off the high-pressure gas inlet, and an upstream connector and a downstream connector adapted to connect the pressure regulator to and integrate it into any gas circuit supplying, on its upstream side, the high-pressure gas and, on the downstream side of the pressure regulator, said low-pressure gas, and such as: - the said inlet duct and the said outlet duct are situated in and discharge into the upstream connector and the downstream connector, respectively, and these two connectors (6,7), disposed coaxially, are adapted to connect the pressure regulator in line to said circuit, - the said inverted gas pressure regulator includes a hollow body constituted of two coaxial hollow parts, referred to as the upstream part on the high-pressure side and the downstream part on the low-pressure side, nested and screwed in one another, - and the mobile regulation part includes a head delimiting, in the hollow part farthest inside the hollow body, the variable-volume gas-tight expansion chamber, and a rod of smaller section that the head to which it is fastened and which slides in a gas-tight manner in the bottom of the upstream part, the distal end of this rod coming to bear against an abutment seal in the position with the high-pressure gas inlet shut off, and the spring element surrounding the rod bearing on one side against the head of the piston and on the other side against the bottom of the upstream hollow part through which the rod slides, characterized in that: - the high-pressure gas inlet duct is situated on the same side as the upstream connector and in the position with the high-pressure gas inlet shut off discharges laterally against the distal end of the rod of the mobile regulation part that performs said shutting off, and in this position the high-pressure gas does not act so directly on the mobile regulation element, but perpendicularly to the axis along which the member allowing the gas to feed the chamber at the low pressure, - the effective contact area on the high-pressure gas side, perpendicular to the mobile regulation part, and which is the only one acting, therefore even becomes extremely low, if not zero. - the said inlet duct and the said outlet duct are situated in and discharge into the upstream connector and the downstream connector, respectively, and these two connectors (6,7), disposed coaxially, are adapted to connect the pressure regulator in line to said circuit, - the said inverted gas pressure regulator includes a hollow body constituted of two coaxial hollow parts, referred to as the upstream part on the high-pressure side and the downstream part on the low-pressure side, nested and screwed in one another, - and the mobile regulation part includes a head delimiting, in the hollow part farthest inside the hollow body, the variable-volume gas-tight expansion chamber, and a rod of smaller section that the head to which it is fastened and which slides in a gas-tight manner in the bottom of the upstream part, the distal end of this rod coming to bear against an abutment seal in the position with the high-pressure gas inlet shut off, and the spring element surrounding the rod bearing on one side against the head of the piston and on the other side against the bottom of the upstream hollow part through which the rod slides, - the high-pressure gas inlet duct is situated on the same side as the upstream connector and in the position with the high-pressure gas inlet shut off discharges laterally against the distal end of the rod of the mobile regulation part that performs said shutting off, and in this position the high-pressure gas does not act so directly on the mobile regulation element, but perpendicularly to the axis along which the member allowing the gas to feed the chamber at the low pressure, - the effective contact area on the high-pressure gas side, perpendicular to the mobile regulation part, and which is the only one acting, therefore even becomes extremely low, if not zero.