Magnetocaloric thermal device including a magnetic field generator (1, 10, 100, 1000) with at least one assembly of anisotropic permanent magnets (30, 31) arranged to create a magnetic flux and defining an air gap wherein said magnetic flux is concentrated. - said assembly including a first element and a second element comprising each at least three permanent magnets (30, 31), - said first and second elements being mounted opposite to each other, symmetrically with respect to a symmetry plane (A-A) and being substantially arranged in a same plane and at least partly respectively surrounded by magnetic field closing elements (51, 52), - the permanent magnets (30, 31) forming the first and second elements of said assembly having the shape of polyhedral blocks held in position laterally with respect to each other by positioning means in surface contact with said permanent magnets (30, 31), - the permanent magnets (30, 31) of said first and second elements of said assembly being arranged substantially in an circular arc according to three zones, a central zone arranged in front of the air gap, a first lateral zone, arranged on one side of said central zone and a second lateral zone arranged on the other side of said central zone, and - the permanent magnets (30, 31) of said first and second lateral zones having magnetization directions opposite with respect to said symmetry plane (A-A), device characterized in that: - said first and second element are mounted on either side of at least two parts out of ferromagnetic material and forming a magnetic flux concentrator device, said parts out of ferromagnetic material and being arranged on either side of said air gap, respectively between the permanent magnets (30, 31) of said first lateral zones of the first and of the second elements of assembly arranged on one side of said central zones, and between the permanent magnets (30, 31) of said second lateral zones of the first and of the second elements of assembly arranged on the other side of said central zones, - each of said magnetic field closing elements (51, 52) of said first and second elements of said assembly has substantially the internal profile of a circular arc that corresponds to the circular arc arrangement according to the three zones (60, 70, 80) of permanent magnets (30, 31) of said first and second elements of said assembly, and - said permanent magnets (30, 31) are arranged, in said assembly, so that, in said central zone, the orientation of their magnetic field lines is at least approximately tangential to the adjacent surface of the closing element (51, 52) of the corresponding magnetic field, and that, in said first and second lateral zones (70, 80), the orientation of their magnetic field lines is perpendicular to the corresponding surface of the closing element (51, 52) of the corresponding magnetic field. - said assembly including a first element and a second element comprising each at least three permanent magnets (30, 31), - said first and second elements being mounted opposite to each other, symmetrically with respect to a symmetry plane (A-A) and being substantially arranged in a same plane and at least partly respectively surrounded by magnetic field closing elements (51, 52), - the permanent magnets (30, 31) forming the first and second elements of said assembly having the shape of polyhedral blocks held in position laterally with respect to each other by positioning means in surface contact with said permanent magnets (30, 31), - the permanent magnets (30, 31) of said first and second elements of said assembly being arranged substantially in an circular arc according to three zones, a central zone arranged in front of the air gap, a first lateral zone, arranged on one side of said central zone and a second lateral zone arranged on the other side of said central zone, and - the permanent magnets (30, 31) of said first and second lateral zones having magnetization directions opposite with respect to said symmetry plane (A-A), - said first and second element are mounted on either side of at least two parts out of ferromagnetic material and forming a magnetic flux concentrator device, said parts out of ferromagnetic material and being arranged on either side of said air gap, respectively between the permanent magnets (30, 31) of said first lateral zones of the first and of the second elements of assembly arranged on one side of said central zones, and between the permanent magnets (30, 31) of said second lateral zones of the first and of the second elements of assembly arranged on the other side of said central zones, - each of said magnetic field closing elements (51, 52) of said first and second elements of said assembly has substantially the internal profile of a circular arc that corresponds to the circular arc arrangement according to the three zones (60, 70, 80) of permanent magnets (30, 31) of said first and second elements of said assembly, and - said permanent magnets (30, 31) are arranged, in said assembly, so that, in said central zone, the orientation of their magnetic field lines is at least approximately tangential to the adjacent surface of the closing element (51, 52) of the corresponding magnetic field, and that, in said first and second lateral zones (70, 80), the orientation of their magnetic field lines is perpendicular to the corresponding surface of the closing element (51, 52) of the corresponding magnetic field.