The invention relates to a device for unlocking swing-action side walls (2 to 5) which are hinged on the base (6) of boxes and/or containers (1), of which the two opposite end walls (4, 5) can be locked to the two adjacent side walls (2, 3) and unlocking takes place by virtue of a lifting movement of a bracket-like actuator (13), which interacts with a movement-deflecting means (16, 17), and wherein unlocking crosspieces (19) act on spring-tongue-like locking means (10) of the side walls (4, 5), these locking means being latched into the end walls (2, 3), and force them out of their latching seat, in which they clamp the end walls (2, 3). According to the invention, the actuator (13) is arranged in a sliding wall element (26) which can be displaced vertically parallel to the end wall (4, 5) in an upwardly open wall cutout of the end wall (4, 5), in lateral guides (25a, 25b) of the wall cutout, these guides continuing the end wall (4, 5), into a position in which it closes the wall cutout or releases the same, and wherein, during displacement movements of the sliding wall element (26), the movement-deflecting means (17, 18, 19), which interact with the ends of the actuator (13), remain in their installation position in the end wall (4, 5) laterally adjacent to the wall cutout.