Adjustable fluid emitter, particularly intended to be used in irrigation systems, which emitter comprises: a casing externally delimiting a volume which is divided into a first chamber and into a second chamber by a membrane that can be elastically deformed; an inlet that can be connected to a fluid supplying source and communicating with said first chamber; an outlet communicating with said second chamber; said first and said second chamber being in communication one with the other by means of at least a communicating duct; a flange for retaining in a fixed position said membrane dividing the first chamber from the second chamber and allowing said membrane to be elastically deformed when said membrane is subjected to a fluid pressure difference between said first chamber and said second chamber, said membrane being free from any passage opening for the fluid from the first to the second chamber (C1, C2), said membrane being adapted to be deformed such that at least a portion thereof changes its position with respect to said outlet, modifying the flow rate of the fluid through said outlet depending on the pressure difference and so on the deformation of the membrane that goes closer or farther away from the outlet so the flow rate of the fluid through said outlet is controlled and kept constant by said membrane despite variations in the fluid pressure at least at the inlet or outlet, said emitter further comprises means (101, 201) for changing the position of the membrane with respect to the outlet, i.e. for mechanically and firmly changing the distance of said membrane from the outlet and/or means (6, 20) for mechanically and firmly changing the elastic behaviour of the membrane and/or for generating a firm deformation of said membrane, characterized in that the membrane is supported by an intermediate flange of the inner space of the casing between two opposite walls (101, 201) one of which has the fluid inlet port and the other one has the outlet port, said two opposite walls being each one a part of a cup-like half-shell and the two cup-like half-shells being tightly coupled together and being movable so that they can go closer or farther away one with respect to the other and particularly said opposite walls (101, 201), while only one of the two half-shells, particularly the half-shell having the wall wherein the inlet is provided, bears the flange fastening the membrane. a casing externally delimiting a volume which is divided into a first chamber and into a second chamber by a membrane that can be elastically deformed; an inlet that can be connected to a fluid supplying source and communicating with said first chamber; an outlet communicating with said second chamber; said first and said second chamber being in communication one with the other by means of at least a communicating duct; a flange for retaining in a fixed position said membrane dividing the first chamber from the second chamber and allowing said membrane to be elastically deformed when said membrane is subjected to a fluid pressure difference between said first chamber and said second chamber, said membrane being free from any passage opening for the fluid from the first to the second chamber (C1, C2), said membrane being adapted to be deformed such that at least a portion thereof changes its position with respect to said outlet, modifying the flow rate of the fluid through said outlet depending on the pressure difference and so on the deformation of the membrane that goes closer or farther away from the outlet so the flow rate of the fluid through said outlet is controlled and kept constant by said membrane despite variations in the fluid pressure at least at the inlet or outlet, said emitter further comprises means (101, 201) for changing the position of the membrane with respect to the outlet, i.e. for mechanically and firmly changing the distance of said membrane from the outlet and/or means (6, 20) for mechanically and firmly changing the elastic behaviour of the membrane and/or for generating a firm deformation of said membrane, characterized in that the membrane is supported by an intermediate flange of the inner space of the casing between two opposite walls (101, 201) one of which has the fluid inlet port and the other one has the outlet port, said two opposite walls being each one a part of a cup-like half-shell and the two cup-like half-shells being tightly coupled together and being movable so that they can go closer or farther away one with respect to the other and particularly said opposite walls (101, 201), while only one of the two half-shells, particularly the half-shell having the wall wherein the inlet is provided, bears the flange fastening the membrane.