A continuously variable transmission comprising: - a first and a second main shaft (1, 2), having respective rotation axes (1a, 2a) fixed and coplanar with respect to a reference plane, said main shafts (1, 2) being each provided with a primary roll surface (13, 23) shaped as a solid of revolution; - at least one auxiliary shaft (3, 3', 3"), rotatable around a respective axis of rotation (3a, 3'a, 3"a), said auxiliary shaft (3, 3', 3") being interposed between said main shafts (1, 2) and provided with two secondary roll surfaces (31, 32) each shaped as a solid of revolution and placed in contact, each one, with a respective primary roll surface (13, 23) of the main shafts (1, 2), so as to transmit the motion from a main shaft to the other main shaft, said auxiliary shaft (3, 3', 3") being configured so that its own rotation axis (3a, 3'a, 3"a) is movable only along a reference plane identified by the rotation axes (1a, 2a) of the two main shafts (1, 2); characterized in that the primary roll surfaces (13, 23) are shaped such that: - in said reference plane, the line tangent to the primary roll surface of the first main shaft and to the corresponding secondary roll surface of the auxiliary shaft in the contact point between said roll surfaces (13, 31) passes through the intersection point between the rotation axis of said first main shaft and the rotation axis of said auxiliary shaft; and - in said reference plane, the line tangent to the primary roll surface of the second main shaft and to the corresponding secondary roll surface of the auxiliary shaft in the contact point between said roll surfaces (23, 32) passes through the intersection point between the rotation axis of said second main shaft and the rotation axis of said auxiliary shaft; and - the intersection point between the rotation axis of said first main shaft and the rotation axis of said auxiliary shaft is distinct from the intersection point between the rotation axis of said second main shaft and the rotation axis of said auxiliary shaft; so that the secondary roll surfaces (31, 32) of the auxiliary shaft roll without rubbing and without prying motion on the respective primary roll surfaces (13, 23) of the main shafts (1, 2), in all operating conditions. - a first and a second main shaft (1, 2), having respective rotation axes (1a, 2a) fixed and coplanar with respect to a reference plane, said main shafts (1, 2) being each provided with a primary roll surface (13, 23) shaped as a solid of revolution; - at least one auxiliary shaft (3, 3', 3"), rotatable around a respective axis of rotation (3a, 3'a, 3"a), said auxiliary shaft (3, 3', 3") being interposed between said main shafts (1, 2) and provided with two secondary roll surfaces (31, 32) each shaped as a solid of revolution and placed in contact, each one, with a respective primary roll surface (13, 23) of the main shafts (1, 2), so as to transmit the motion from a main shaft to the other main shaft, said auxiliary shaft (3, 3', 3") being configured so that its own rotation axis (3a, 3'a, 3"a) is movable only along a reference plane identified by the rotation axes (1a, 2a) of the two main shafts (1, 2); characterized in that the primary roll surfaces (13, 23) are shaped such that: - in said reference plane, the line tangent to the primary roll surface of the first main shaft and to the corresponding secondary roll surface of the auxiliary shaft in the contact point between said roll surfaces (13, 31) passes through the intersection point between the rotation axis of said first main shaft and the rotation axis of said auxiliary shaft; and - in said reference plane, the line tangent to the primary roll surface of the second main shaft and to the corresponding secondary roll surface of the auxiliary shaft in the contact point between said roll surfaces (23, 32) passes through the intersection point between the rotation axis of said second main shaft and the rotation axis of said auxiliary shaft; and - the intersection point between the rotation axis of said first main shaft and the rotation axis of said auxiliary shaft is distinct from the intersection point between the rotation axis of said second main shaft and the rotation axis of said auxiliary shaft; so that the secondary roll surfaces (31, 32) of the auxiliary shaft roll without rubbing and without prying motion on the respective primary roll surfaces (13, 23) of the main shafts (1, 2), in all operating conditions. - in said reference plane, the line tangent to the primary roll surface of the first main shaft and to the corresponding secondary roll surface of the auxiliary shaft in the contact point between said roll surfaces (13, 31) passes through the intersection point between the rotation axis of said first main shaft and the rotation axis of said auxiliary shaft; and - in said reference plane, the line tangent to the primary roll surface of the second main shaft and to the corresponding secondary roll surface of the auxiliary shaft in the contact point between said roll surfaces (23, 32) passes through the intersection point between the rotation axis of said second main shaft and the rotation axis of said auxiliary shaft; and - the intersection point between the rotation axis of said first main shaft and the rotation axis of said auxiliary shaft is distinct from the intersection point between the rotation axis of said second main shaft and the rotation axis of said auxiliary shaft; so that the secondary roll surfaces (31, 32) of the auxiliary shaft roll without rubbing and without prying motion on the respective primary roll surfaces (13, 23) of the main shafts (1, 2), in all operating conditions.