A packaging machine comprises a movable body having mandrels and intermittently drivable so as to stop each of the mandrels at a process station while carrying containers as fitted around the respective mandrels with a bottom forming portion of each container projecting outward from the mandrel, and a bottom breaker for forming folds in a bottom forming end portion of the container fitted around the mandrel as halted at the process station so as to render the end portion foldable flat. The bottom breaker has first folding means for initially folding the second and fourth bottom panels in two into triangles, and second folding means for subsequently folding first and third bottom panels. The second folding means has an upstream arm movable into pressing contact with the first bottom panel, and a downstream arm movable into pressing contact with the third bottom panel. The downstream arm is provided with a pressure plate at a portion thereof to be contacted with the third bottom panel.