Breaking device, to break attachment zones defining lines which can be broken on cardboard sheets stacked forming a stack, the breaking device comprising at least: - an upper pressing member which is mobile at least between: • an immobilisation position, wherein the upper pressing member exerts a pressure against the upper sheet of the stack, so as to immobilise the stack, and • a clearing position, wherein the upper pressing member is arranged so as to be separate from the upper sheet of the stack; and - a support portion configured to support the stack when the upper pressing member is in the immobilisation position, the support portion comprising a plurality of transport members configured to transport and move the stack along a transport direction, the transport members being juxtaposed along a transversal direction which extends transversally to the transport direction, several transport members each including: i) a belt extended parallel to the transport direction and configured to drive the stack along the transport direction, ii) at least one rotating pinion configured to drive the belt on a belt circuit, characterised: - in that, the transport members are configured such that two juxtaposed transport members can be moved against one another along the transversal direction, and - in that, it further comprises a lower pressing member arranged under the transport members, the transport members being mobile at least between: • an immobilisation position, wherein the lower pressing member exerts a pressure against lower faces of the transport members, such that the transport members immobilise the stack, and • a clearing position, wherein the lower pressing member is arranged so as to be separate from the lower faces of the transport members; the lower pressing member comprising: i) two lower plates (6.1, 6.2), adjacent and expandable from one another along the transversal direction so as to define a breaking slot (2.0), and ii) a lower translation actuator (6.3) arranged to move the lower plates (6.1, 6.2) in translation along the transversal direction, so as to make the breaking slot (2.0) coincide with a breakable line. - an upper pressing member which is mobile at least between: • an immobilisation position, wherein the upper pressing member exerts a pressure against the upper sheet of the stack, so as to immobilise the stack, and • a clearing position, wherein the upper pressing member is arranged so as to be separate from the upper sheet of the stack; and • an immobilisation position, wherein the upper pressing member exerts a pressure against the upper sheet of the stack, so as to immobilise the stack, and • a clearing position, wherein the upper pressing member is arranged so as to be separate from the upper sheet of the stack; - a support portion configured to support the stack when the upper pressing member is in the immobilisation position, the support portion comprising a plurality of transport members configured to transport and move the stack along a transport direction, the transport members being juxtaposed along a transversal direction which extends transversally to the transport direction, several transport members each including: i) a belt extended parallel to the transport direction and configured to drive the stack along the transport direction, ii) at least one rotating pinion configured to drive the belt on a belt circuit, - in that, the transport members are configured such that two juxtaposed transport members can be moved against one another along the transversal direction, and - in that, it further comprises a lower pressing member arranged under the transport members, the transport members being mobile at least between: • an immobilisation position, wherein the lower pressing member exerts a pressure against lower faces of the transport members, such that the transport members immobilise the stack, and • a clearing position, wherein the lower pressing member is arranged so as to be separate from the lower faces of the transport members; the lower pressing member comprising: i) two lower plates (6.1, 6.2), adjacent and expandable from one another along the transversal direction so as to define a breaking slot (2.0), and ii) a lower translation actuator (6.3) arranged to move the lower plates (6.1, 6.2) in translation along the transversal direction, so as to make the breaking slot (2.0) coincide with a breakable line. • an immobilisation position, wherein the lower pressing member exerts a pressure against lower faces of the transport members, such that the transport members immobilise the stack, and • a clearing position, wherein the lower pressing member is arranged so as to be separate from the lower faces of the transport members; the lower pressing member comprising: i) two lower plates (6.1, 6.2), adjacent and expandable from one another along the transversal direction so as to define a breaking slot (2.0), and ii) a lower translation actuator (6.3) arranged to move the lower plates (6.1, 6.2) in translation along the transversal direction, so as to make the breaking slot (2.0) coincide with a breakable line. i) two lower plates (6.1, 6.2), adjacent and expandable from one another along the transversal direction so as to define a breaking slot (2.0), and ii) a lower translation actuator (6.3) arranged to move the lower plates (6.1, 6.2) in translation along the transversal direction, so as to make the breaking slot (2.0) coincide with a breakable line.