A double-reeved lifting device for a lifting machinery, such as for example a crane, comprising two reeve blocks (3, 4), namely a lower reeve block secured to a lifting hook and an upper reeve block, wherein the two reeve blocks (3, 4) comprise reversible connection means adapted to be reversibly configured between: - a connected configuration in which the upper reeve block is connected to the lower reeve block so as to be able to accompany it in ascending/descending movements along a main axis, and - a disconnected configuration in which the upper reeve block is disconnected from the lower reeve block so as to be able to remain hanging above the lower reeve block which could perform descending/ascending movements without the upper reeve block, wherein the connected configuration and the disconnected configuration respectively correspond to a double-reeved configuration and to a simple-reeved configuration, or vice versa, of the double-reeved lifting device, wherein the reversible connection means comprise a locking mechanism mounted on one of the two reeve blocks (3, 4), and a complementary locking structure mounted on the other one of the two reeve blocks (3, 4) and adapted to cooperate with the locking mechanism; wherein the complementary locking structure comprises a frame securely supporting a bolt formed at least partially by a shaft extending transversely to the main axis, and wherein the locking mechanism comprises: - a chassis comprising a locking channel having an elongated shape along the main axis and provided with a mouthpiece through which the bolt could come in and come out of the locking channel and could slide in the locking channel in an entry direction and in an exit direction, opposite to the entry direction, respectively upon a relative approach or distancing between the two reeve blocks (3, 4), and said double-reeved lifting device being characterized in that - at least one latch pivotally mounted on the chassis about a pivot axis so as to pivot inside the locking channel, said latch being provided with a concave-shaped free end adapted to engage with the bolt, and being coupled to an elastic biasing element urging said latch towards a neutral position. - a connected configuration in which the upper reeve block is connected to the lower reeve block so as to be able to accompany it in ascending/descending movements along a main axis, and - a disconnected configuration in which the upper reeve block is disconnected from the lower reeve block so as to be able to remain hanging above the lower reeve block which could perform descending/ascending movements without the upper reeve block, wherein the connected configuration and the disconnected configuration respectively correspond to a double-reeved configuration and to a simple-reeved configuration, or vice versa, of the double-reeved lifting device, wherein the reversible connection means comprise a locking mechanism mounted on one of the two reeve blocks (3, 4), and a complementary locking structure mounted on the other one of the two reeve blocks (3, 4) and adapted to cooperate with the locking mechanism; wherein the complementary locking structure comprises a frame securely supporting a bolt formed at least partially by a shaft extending transversely to the main axis, and wherein the locking mechanism comprises: - a chassis comprising a locking channel having an elongated shape along the main axis and provided with a mouthpiece through which the bolt could come in and come out of the locking channel and could slide in the locking channel in an entry direction and in an exit direction, opposite to the entry direction, respectively upon a relative approach or distancing between the two reeve blocks (3, 4), and - a chassis comprising a locking channel having an elongated shape along the main axis and provided with a mouthpiece through which the bolt could come in and come out of the locking channel and could slide in the locking channel in an entry direction and in an exit direction, opposite to the entry direction, respectively upon a relative approach or distancing between the two reeve blocks (3, 4), and - at least one latch pivotally mounted on the chassis about a pivot axis so as to pivot inside the locking channel, said latch being provided with a concave-shaped free end adapted to engage with the bolt, and being coupled to an elastic biasing element urging said latch towards a neutral position.