a sliding device for a storage case is provided which is durable and provides a smooth sliding motion even in environments , such as those encountered in a refrigerator , wherein the storage case is subjected to humid , cold conditions . the sliding device comprises a fixed rail fixedly mounted to an inner side surface of the storage case and having a roller coupling portion in which a first set of rollers are rollably received ; a movable rail fixedly mounted to an outer side surface of the storage container and having a roller coupling portion in which a set of second rollers are rollably received ; and a middle rail which is slidably mounted between the fixed rail and the movable rail so as to provide a coupling relationship therebetween which guides the rolling motion of the first and second rollers . the fixed rail , the movable rail and the middle rail , as well as the rollers , are made of an injection molded plastic .