A locking device for locking tools in a press brake includes a first jaw (2) and a second jaw (3), movable towards and away from each other, and at least one safety hook (4) interposed there between provided with a retaining tooth (41) adapted to be inserted into a groove (52) defined in the shank (51) of a tool (5), wherein on an inner side (35) of the second jaw (3) facing the first jaw (2) there is provided at least one thrust surface (36) adapted to cooperate with, while resting slidingly against, at least one corresponding rest surface (43) on an outer side (42) of the safety hook, the thrust surface (36) and the rest surface (43) lying substantially parallel along a thrust plane (P) sloping in the opposite direction to the first jaw (2) by an angle (α) of between 30° and 60° with respect to a vertical plane.