The corrosion resin-casts and the tissue preparations (Azan staining) of the digestive diverticula in the Japanese paper-bubble, Haloa japonica, were observed. The digestive diverticula were located around the stomach except on the dorsal side. Three ducts were located at each orifice of the stomach. The duct did not ramify. Three thick tubules which resembled a duct of digestive diverticula extended to the end of the each duct and were branching out. Thin tubules extended from the walls of the three thick tubules. The observations revealed that the structure of the digestive diverticula in the Japanese paper-bubble (Opisthobranchia : Cephalaspidea) closely resemble that of Prosobranchia (Vetigastropoda).