A packing device according to an embodiment includes a supply station, a right end effector, a left end effector, a right arm unit, a left arm unit, and a forming station. A cardboard box in a flat state is placed on the supply station. The cardboard box developed three-dimensionally is placed on the forming station. The right arm unit includes the right end effector provided with a suction unit. The left arm unit includes the left end effector provided with a suction unit. The packing device performs an operation of developing the cardboard box and an operation of moving the cardboard box to the forming station by using the right arm unit and the left arm unit while sucking both side surfaces of the cardboard box placed on the supply station by using the suction units.