An inner volatile atmospheric substance diffuser which comprises: - two outer walls (2a, 2b), each having an outer face and an inner face, which are spaced apart and mutually opposite and parallel to each other, • one face of which being pervious to the volatile substance, in the transversal direction, from side to side, • one face of which, in at least one shape-changing release area, can change shape in the transversal direction, and the outside-inside direction, further to a sufficient release pressure along the same direction and in the same orientation, manually exerted by the user of the diffuser to activate the diffusion; - an inner plate positioned between and opposite the two outer walls (2a, 2b), adjacent to the inner face of the pervious outer wall (2a, 2b), and forming with the two outer walls (2a, 2b), a rigidly connected assembly limited by two faces, • provided with gaps communicating with each other and opening on such faces, and compressible in the transverse direction, • and provided with a cavity therein, above a shape-changing release area, which receives and holds a volatile substance capsule in position, - at least one volatile substance capsule which, whether it is one unit or consists of a set of several elementary capsules, • in the integrity thereof, contains a volatile substance and is adjacent to the inner plate and to the inner face of the pervious outer wall (2a, 2b), • which is breakable by means of a sufficient transversal pressure, which corresponds to the release pressure exerted by the user, thus releasing the volatile substance, such that: - before use, the volatile substance capsule has its integrity, - in order to trigger the diffusion of the volatile substance from a volatile substance capsule, and thus to activate the diffuser, the user exerts the release pressure onto the shape-changing release area which corresponds to the capsule, thus breaking said capsule and releasing the volatile substance that diffuses towards the inner face of the pervious outer wall (2a, 2b), directly on the one hand and indirectly on the other hand via the communicating gaps and on the faces of the inner plate, then diffuses through the pervious outer wall (2a, 2b) and then into the surrounding atmosphere. - two outer walls (2a, 2b), each having an outer face and an inner face, which are spaced apart and mutually opposite and parallel to each other, • one face of which being pervious to the volatile substance, in the transversal direction, from side to side, • one face of which, in at least one shape-changing release area, can change shape in the transversal direction, and the outside-inside direction, further to a sufficient release pressure along the same direction and in the same orientation, manually exerted by the user of the diffuser to activate the diffusion; • one face of which being pervious to the volatile substance, in the transversal direction, from side to side, • one face of which, in at least one shape-changing release area, can change shape in the transversal direction, and the outside-inside direction, further to a sufficient release pressure along the same direction and in the same orientation, manually exerted by the user of the diffuser to activate the diffusion; - an inner plate positioned between and opposite the two outer walls (2a, 2b), adjacent to the inner face of the pervious outer wall (2a, 2b), and forming with the two outer walls (2a, 2b), a rigidly connected assembly limited by two faces, • provided with gaps communicating with each other and opening on such faces, and compressible in the transverse direction, • and provided with a cavity therein, above a shape-changing release area, which receives and holds a volatile substance capsule in position, • provided with gaps communicating with each other and opening on such faces, and compressible in the transverse direction, • and provided with a cavity therein, above a shape-changing release area, which receives and holds a volatile substance capsule in position, - at least one volatile substance capsule which, whether it is one unit or consists of a set of several elementary capsules, • in the integrity thereof, contains a volatile substance and is adjacent to the inner plate and to the inner face of the pervious outer wall (2a, 2b), • which is breakable by means of a sufficient transversal pressure, which corresponds to the release pressure exerted by the user, thus releasing the volatile substance, • in the integrity thereof, contains a volatile substance and is adjacent to the inner plate and to the inner face of the pervious outer wall (2a, 2b), • which is breakable by means of a sufficient transversal pressure, which corresponds to the release pressure exerted by the user, thus releasing the volatile substance, - before use, the volatile substance capsule has its integrity, - in order to trigger the diffusion of the volatile substance from a volatile substance capsule, and thus to activate the diffuser, the user exerts the release pressure onto the shape-changing release area which corresponds to the capsule, thus breaking said capsule and releasing the volatile substance that diffuses towards the inner face of the pervious outer wall (2a, 2b), directly on the one hand and indirectly on the other hand via the communicating gaps and on the faces of the inner plate, then diffuses through the pervious outer wall (2a, 2b) and then into the surrounding atmosphere.