An opening system including a cutting device for cutting an adhesive tape; a suctioning and lifting device for suctioning a upper panels, which are separated from each other because the adhesive tape is cut by the cutting device; rod members which are elongated to be inserted into gaps, when the gaps are formed between the upper panels and upper edges of side surfaces in the packaging box because the upper panels are spaced apart from the side panels by the suctioning and lifting device; and an opening device which moves the respective rod members while being in contact with lower surfaces of the upper panels such that the upper panels are rotated outward with respect to boundaries between the upper panels and the side panels.