Abstract: A method is disclosed which makes a bag-in-carton by successively and intermittently advancing cartons, the upper ends of which are opened, and during the advancement successively supplying each of the cartons with a flattened bag, and subsequently blowing up the bag. A bag supplying apparatus and a bag blowing up apparatus used for performing the method are also disclosed. The bag supplying apparatus comprises means for supplying tubular material, roller means for intermittently advancing the material, means for providing the material with side folds while the material is being advanced, means for heat sealing the side folded material thereacross at the places spaced by the distance equal to the desired length of the bag to form bottom seams, and means for cutting the material just below the bottom seams to provide bags.