Abstract: A positioning device includes two guiding members fixed spacedly in a housing. Each guiding member has a hook-shaped guiding slot having an elongate first slot portion, and a curved second slot portion defined by parallel first and second guiding faces. A pivot member is connected pivotally to a detachable module. Two positioning rods of the pivot member are guided respectively by the first slot portions to move rearwardly as a result of rearward movement of the detachable module until the positioning rods abut respectively against the first guiding faces. The pivot member may then be pivoted such that the positioning rods are in slidable contact with the second guiding faces, and move along the second slot portions, respectively, thereby resulting in further rearward movement of the detachable module by a predetermined distance.