The pneumatic logic circuit is of generally symmetrical structure around an axis and symmetrical with respect to a median plane normal to this axis. It has a median plate provided with an axial passage and with a duct opening into this passage. On each side of the median plane is a diaphragm constituted by a flat sheet of rubber or of synthetic elastomer with, on its outer surface, a centering shoulder and with an axial cylindrical passage. It comprises axially a piston rod, passing freely through said passage of the median plate and with fluid-tightness through said passages of the diaphragm and bearing two pistons. On each side of the median plane is a bushing, bearing on the diaphragm and capping the centering shoulder thereof and allowing the piston to pass, each diaphragm being provided on its inner surface with an axial impression, comprising at the center a cylindrical chamber, whose diameter is a little greater than the diameter of said axial passage of the median plate, and a toric groove, separated from said cylindrical chamber by an annular lip with a flat profile capable of bearing against said median plate. These pistons each bear against the outer surface of the corresponding diaphragm. On each side of the median plane is an elastic diaphragm and a base applied against the corresponding bushing, and on each side a duct passes through the median plate and opens into the corresponding toric groove. The circuit is useful for numerical computers and control systems.