Device for dehumidifying the structure of a building, said device comprising: - an inner member made of conductive material comprising a main body in which at least one capturing element is arranged oriented along a first axis, and at least one lateral body fixed to the main body in which a reflection element is arranged oriented along a second axis arranged inclined with respect to said first axis, said capturing and reflection elements both comprising a first cylindrical portion (20, 30) arranged at one end of the main body and of the lateral body, respectively, a second frustoconical portion (21, 31) and a third cylindrical portion (22, 32) with diameter smaller than the diameter of the first portion (20, 30), said first, second and third portion (20, 21, 22, 30, 31, 32) being coaxial, and said second frustoconical portion (21, 31) narrowing from the first portion (20, 30) to the third portion (22, 32), said main body comprising a transverse through hole which extends parallel to the axis adapted for insertion of a first fastening member for the fastening of said at least one lateral body to the main body, said first fastening member passing axially through said at least one reflection element, said lateral body comprising an axial through hole adapted to permit the insertion of said first fastening member for the fastening of said at least one lateral body to the main body, and the axial through hole being provided along the axis as the extension of the third portion of the reflection element; - an outer container comprising a parallelepipedal body made of aluminium, and two shaped covers for closing the container, said main body being fastened in use to one of the two covers by means of a second fastening member. - an inner member made of conductive material comprising a main body in which at least one capturing element is arranged oriented along a first axis, and at least one lateral body fixed to the main body in which a reflection element is arranged oriented along a second axis arranged inclined with respect to said first axis, said capturing and reflection elements both comprising a first cylindrical portion (20, 30) arranged at one end of the main body and of the lateral body, respectively, a second frustoconical portion (21, 31) and a third cylindrical portion (22, 32) with diameter smaller than the diameter of the first portion (20, 30), said first, second and third portion (20, 21, 22, 30, 31, 32) being coaxial, and said second frustoconical portion (21, 31) narrowing from the first portion (20, 30) to the third portion (22, 32), said main body comprising a transverse through hole which extends parallel to the axis adapted for insertion of a first fastening member for the fastening of said at least one lateral body to the main body, said first fastening member passing axially through said at least one reflection element, said lateral body comprising an axial through hole adapted to permit the insertion of said first fastening member for the fastening of said at least one lateral body to the main body, and the axial through hole being provided along the axis as the extension of the third portion of the reflection element; - an outer container comprising a parallelepipedal body made of aluminium, and two shaped covers for closing the container, said main body being fastened in use to one of the two covers by means of a second fastening member.