A box packing apparatus is equipped with a first conveyor, a parallel link robot, and a flap folding mechanism. The first conveyor conveys an article. The parallel link robot takes hold of the article on the first conveyor and carries it into a cardboard box that has an upper opening. The flap folding mechanism folds open to the outside of the upper opening at least one of plural cover flaps of the cardboard box that are located around the upper opening.