Constraint device for the releasable fastening of a child safety seat to a motor vehicle seat

A constraint device (1) for the releasable fastening of a child safety seat (2) to a motor vehicle seat (3) is described, equipped with fastening means (5) for coupling with matching means (14) carried by the seat (3); control means (6) operatively connected to the fastening means (5) and mobile for defining coupling and decoupling between the fastening means (5) and the matching means (14); and guiding means (7) for defining a predetermined movement path for the control means (6). Such path includes a first section (P1), along which the operation of the fastening means (5) is prevented, and a second section (P2), along which the operation of the fastening means (5) by the control means (6) is allowed.