A stocker system and a method of managing a stocker, the stocker system including a stocker, a rack master, and a sensor to easily examine a shelf of the stocker. The stocker includes the shelf on which a product is loaded. The rack master includes a body part and an arm part connected to the body part to move the product toward or away from the stocker. The sensor unit faces the shelf when the arm part is moved above or below the shelf and the sensor unit is disposed on the arm part. The sensor unit includes a facing surface that is not in contact with the arm part. A plurality of displacement sensors is disposed on the facing surface of the sensor unit to measure relative positions between the sensor unit and the shelf at a plurality of positions.